Abstract:
A method of determining the shift lever position of an electronic automatic transmission system by identifying the mode of transmission operation selected by the driver of the vehicle to provide hysteresis between the park, reverse, neutral, drive and low positions, to permit improved performance and response of the controller and to permit limited operation of the controller upon the occurrence or detection of a fault effecting the performance of the transmission. Such faults include the loss of a PRND2L sensor and the loss of one or more sensors indicative of the dynamics of the vehicle or hydraulic circuit.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates generally to an automatic transmission and more particularly to a method of determining the shift lever position selected by the driver of a transmission that is controlled electronically and hydraulically. 
     2. Discussion 
     Generally speaking, land vehicles require three basic components. These components comprise a power plant (such as an internal combustion engine) a power train and wheels. The internal combustion engine produces force by the conversion of the chemical energy in a liquid fuel into the mechanical energy of motion (kinetic energy). The function of the power train is to transmit this resultant force to the wheels to provide movement of the vehicle. 
     The power train&#39;s main component is typically referred to as the “transmission”. Engine torque and speed are converted in the transmission in accordance with the tractive-power demand of the vehicle. The vehicle&#39;s transmission is also capable of controlling the direction of rotation being applied to the wheels so that the vehicle may be driven both forward and backward. 
     A conventional transmission includes a hydrodynamic torque converter to transfer engine torque from the engine crankshaft to a rotatable input member of the transmission through fluid-flow forces. The transmission also includes frictional units which couple the rotating input member to one or more members of a planetary gearset. Other frictional units, typically referred to as brakes, hold members of the planetary gearset stationary during flow of power. These frictional units are usually brake clutch assemblies or band brakes. The drive clutch assemblies can couple the rotating input member of the transmission to the desired elements of the planetary gearsets, while the brakes hold elements of these gearsets stationary. Such transmission systems also typically provide for one or more planetary gearsets in order to provide various ratios of torque and to ensure that the available torque and the respective tractive power demand are matched to each other. 
     Transmissions are generally referred to as manually actuated or automatic transmissions. Manual transmissions generally include mechanical mechanisms for coupling rotating gears to produce different ratio outputs to the drive wheels. Automatic transmissions are designed to take automatic control of the frictional units, gear ratio selection and gear shifting. A thorough description of general automatic transmission design principals may be found in “Fundamentals of Automatic Transmissions and Transaxles,” Chrysler Corporation Training Manual No. TM-508A. Additional descriptions of automatic transmissions may be found in U.S. Pat. No. 3,631,744, entitled “Hydromatic Transmission,” issued Jan. 4, 1972 to Blomquist, et al., and U.S. Pat. No. 4,289,048, entitled “Lock-up System for Torque Converter,” issued on Sept. 15, 1981 to Mikel, et al. Each of these patents is hereby incorporated by reference. 
     In general, the major components featured in such an automatic transmission are: a torque converter as above-mentioned; fluid pressure-operated multi-plate drive or brake clutches and/or brake bands which are connected to the individual elements of the planetary gearsets in order to perform gear shifts without interrupting the tractive power; one-way clutches in conjunction with the frictional units for optimization of power shifts; and transmission controls such as valves for applying and releasing elements to shift the gears, for enabling power shifting, and for choosing the proper gear, dependent on shift-program selection by the driver, accelerator position, the engine condition and vehicle speed. 
     The control system of the automatic transmission is typically hydraulically operated through several valves which are operable for directing and regulating the supply of pressurized fluid. This hydraulic pressure control will cause either the actuation or deactuation of the respective frictional units for effecting gear changes in the transmission. The valves used in the hydraulic control circuit typically comprise spring-biased spool valves, spring-biased accumulators and ball check valves. Since many of these valves rely upon springs to provide a predetermined amount of force, it will be appreciated that each transmission design represents a finely tuned arrangement of interdependent valve components. While this type of transmission control system has worked well over the years, it does have its limitations. 
     In view of these limitations, several advanced transmission control systems have been proposed. One such system was disclosed in U.S. Pat. No. 3,956,947 to Leising, et al., issued on May 18, 1979, the disclosure of which is hereby incorporated by reference. The automatic transmission disclosed in U.S. Pat. No. 3,956,947 features an adaptive control system that includes electronically operated solenoid-actuated valves for controlling certain fluid pressures. In accordance with this electric/hydraulic control system, the automatic transmission would be responsive to an acceleration factor for controlling the output torque of the transmission during a shift from one ratio of rotation (between the input and output shafts of the transmission) to another. Specifically, the operation of the solenoid-actuated valves would cause a rotational speed versus time curve of a sensed rotational component of the transmission to substantially follow along a predetermined path during shifting. 
     Another advanced transmission control system was disclosed in U.S. Pat. No. 4,965,735 to Holbrook et al., the disclosure of which is hereby incorporated by reference. The system disclosed in U.S. Pat. No. 4,965,735 in an improved adaptive transmission control system utilizes an electronic controller to receive input signals indicative of engine speed, turbine speed, output speed (vehicle speed), throttle angle position, brake application, predetermined hydraulic pressure, the driver selected gear, engine coolant temperature and/or ambient air temperature. The controller generates command signals for causing the actuation of a plurality of solenoid-actuated valves which regulate the application and release of pressure to and from the frictional elements of the transmission system. Accordingly, the controller executes predetermined shift schedules stored in the memory of the controller through appropriate command signals to the solenoid-actuated valves and the feedback which is provided by various input signals. 
     Another significant aspect of U.S. Pat. No. 4,965,735 is the ability to utilize closed-loop feedback to control the transmission. Closed-loop feedback allows the control system to perform its functions based on real-time feedback sensor information. This is particularly advantageous as the control actuation can be corrected as opposed to an open-loop control in which signals to various elements are processed in accordance to a predetermined program. The controller is also programmed to determine the shift lever position of the driver selected gear of the transmission to provide hysteresis between the various gear positions, and to provide limited operation of the transmission in the event the sensors which determine the driver selected gear or operating conditions are not operating properly. 
     Despite these advancements, there remains a need in the art for an improved transmission control system which is more reliable in operation and which provides improved fault detection. Furthermore, there remains a need in the art for an improved transmission control system which provides enhanced functionality despite the existence of a fault within the transmission control system. 
     SUMMARY OF THE INVENTION 
     It is therefore one object of the present invention to provide a transmission control methodology that provides improved response and performance. 
     It is another object of the present invention to provide a transmission control methodology having improved fault detection capabilities. 
     It is a further object of the present invention to provide a transmission control methodology having improved functionality in the event that a fault within the transmission control system. 
     To achieve the foregoing objects, the transmission controller includes an electronic control module which receives input signals indicative of engine speed, turbine speed, vehicle speed, throttle angle position, brake application, predetermined hydraulic pressure, the driver selected gear or operating condition, engine coolant temperature, and/or ambient temperature. The control module generates command or control signals for causing the actuation of a plurality of solenoid-actuated valves which regulate the application and release of pressure to and from the frictional units of the transmission. Accordingly, the control module will execute predetermined shift schedules stored in the memory of the control module through appropriate command signals to the solenoid-actuated valves and the feedback which is provided by various input signals. 
     A primary feature of the present invention is to provide an improved adaptive control methodology based on closed-loop control. This is particularly advantageous because the control actuation can be corrected to accommodate the performance and response of the transmission. Also advantageously, closed-loop control also permits the detection of faults that effect the performance of the transmission to be accurately identified, allowing the control methodology to disregard “suspect” data and control the operation of the transmission using data from inputs which are known to be functioning properly. 
     In accordance with one aspect of the present invention, the controller is programmed to determine the shift lever position of the driver selected gear or operating mode of the transmission to provide hysteresis between the PRND2L positions and to provide limited operation of the transmission in the event the PRND2L sensor or other input devices are not operating properly. 
     Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a schematic diagram of a motor vehicle; 
     FIG. 1B is a schematic diagram of the hydraulic circuitry of the transmission shown in FIG. 1A; 
     FIG. 1C is a diagram showing the PRND2L code produced by the PRND2L sensor; 
     FIG. 2 is a schematic diagram in flowchart form of a portion of the method of the present invention; 
     FIG. 3 is a schematic diagram in flowchart form of another portion of the method of the present invention; 
     FIG. 4 is a schematic diagram in flowchart form of another portion of the method of the present invention; 
     FIG. 5 is a schematic diagram in flowchart form of another portion of the method of the present invention; 
     FIG. 6 is a schematic diagram in flowchart form of another portion of the method of the present invention; 
     FIG. 7 is a schematic diagram in flowchart form of the R-N subroutine; 
     FIG. 8 is a schematic diagram in flowchart form of the N-R subroutine; 
     FIG. 9 is a schematic diagram in flowchart form of the N-D subroutine; 
     FIG. 10 is a schematic diagram in flowchart form of the D-N subroutine; 
     FIG. 11 is a schematic diagram in flowchart form of the D-2/2-D subroutine. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1A, a portion of a motor vehicle  10  is schematically shown. Motor vehicle  10  includes an engine  12 , a torque converter  14  and an automatic-type hydraulic transmission  16  having a plurality of gear ratios  16   a  such as reverse, neutral, overdrive, direct, second and low, an input member  16   b  for receiving a torque input, an output member  16   c  and a transmission controller  18 . The hydraulic circuit  20  of transmission  16  is shown in detail in FIG.  1 B. Hydraulic circuit  20  includes a fluid pump  22 , a plurality of hydraulic conduits  24 , a manual valve  26 , a plurality of pressure switches  28 , a plurality of solenoids  30  each coupled to a directional valve  32 , a plurality of clutches  34  for selectively engaging any of the plurality of gear ratios  16   a , and a plurality of directional spool valves  36 . Generally speaking, pressurized fluid supplied from pump  22  is directed to one or more desired clutches  34  through one or more hydraulic conduits  24  by the efforts of manual valve  26 , and in some circumstances, one or more directional valves  32  and/or one or more directional spool valves  36 . 
     The transmission controller  18  includes a shift lever (not shown), a PRND2L sensor  38 , an electronic control module  40  and a plurality of sensors  42  for producing sensor signals in response to various vehicle dynamics, such as the input and output speeds of transmission  16 . The shift lever is operable for causing manual valve  26  to translate in a linear manner between the R, N, D and 2 positions to thereby cause the flow of pressurized fluid to be directed to one or more desired hydraulic conduits  24 . PRND2L sensor  38  senses the relative position of either the shift lever or manual valve  26  and produces a PRND2L code (PC) indicative of the position of the manual valve  26 . Preferably, PRND2L sensor  38  includes five contact points and produces a PC that corresponds to the PRND2L code shown in FIG.  1 C. As shown, the PC includes codes indicating that manual valve  26  has been position to supply fluid to one or more predetermined conduits  24 . Such codes include P, R, N1, N2, D, 2 and L. The PC also includes codes indicating that manual valve  26  is in transition between two or more predetermined conduits  24 . Such codes include T1, T2, T3, and T4. The last transition code, T5, is used as an electronic control point in the methodology and its generation does not indicate that manual valve  26  is being moved. 
     The transmission controller  18  relies on the Shift Lever Position (SLP) methodology to identify the mode of transmission operation selected by the driver to provide hysteresis between the PRND2L positions, to improve the performance and response of transmission  16  and to permit limited operation of transmission  16  without functioning PRND2L sensor  38  by utilizing pressure switch data from pressure switches  28  to determine the position of manual valve  26 . 
     Referring now to FIG. 2, the SLP methodology of the present invention is entered at bubble  200 . The methodology advances to decision block  204  where the PRND2L data error (PDE) flag is checked. The PDE flag is set if an invalid PRDN2L code (PC) has been maintained for a time exceeding a predetermined PDE time threshold. An invalid PC is obtained when the signal from the PRND2L sensor is not indicative of any of the predetermined shift lever positions. If the PDE flag has not been set (i.e., an invalid PC has not been maintained for a PDE time threshold), the methodology will proceed to decision block  208  where the methodology evaluates the PC. If the PC is invalid, the methodology assumes that the invalid PC is an intermittent condition and proceeds to block  210  where the current shift lever logic position (SLPC) is set to the previous shift lever logic position (SLP0). The methodology then loops back to decision block  204 . Returning to decision block  208 , if the PC is not invalid, the methodology proceeds to decision block  212  where the pressure switch data available (PSD) flag is checked. The PSD flag is used to prevent improper use of the pressure switch data in the SLP methodology. The PSD flag is typically set if hydraulic pressure is available and the pressure switches are capable of providing a reliable signal. 
     If the PSD flag has not been set indicating that data from the pressure switches is not available, the methodology advances to bubble  214  where the methodology continues along branch A which is discussed in detail below. Operation along branch A assumes that the vehicle engine is not running or that there is a failure in the supply of hydraulic fluid, necessitating that the SLP methodology to rely on the PC and SLP0 to change SLPC. If the PSD flag has been set indicating that data from the pressure switches is available, the methodology advances to bubble  218  where the methodology continues along branch B which is discussed in detail below. Operation along branch B is similar to that of branch A, except that pressure switch data is utilized to improve the performance and response of the SLP methodology. 
     Referring back to decision block  204 , if the PDE flag is set indicating that an invalid PC has been maintained for a time exceeding the predetermined PDE time threshold, the methodology proceeds to decision block  220  where the PC is evaluated. If the PC is not invalid, the methodology advances to bubble  222  where the methodology proceeds along branch C which is discussed in detail below. Operation along branch C essentially permits the SLP methodology to interpret the invalid PC in some situations to determine SLPC. If the PC is invalid, the methodology proceeds to block  224  where the PSD flag is checked. 
     If the PSD flag is set in decision block  224 , the methodology advances to bubble  226  and proceeds along branch D which is discussed in detail below. Operation along branch D primarily necessitates that the SLP methodology rely on SLP0 and pressure switch data to determine SLPC. If the PSD flag is not set in decision block  224 , the methodology proceeds to block  228  where SLPC is set to SLP0. The methodology then loops back to decision block  204 . 
     Branch A 
     With reference to FIG. 3, the methodology proceeds along branch A to decision block  300  where the methodology analyzes the PC. If the PC is indicative of the R, T1 or T2 positions, the methodology selects R as SLPC. The methodology proceeds to bubble  216  where subroutine A terminates and the methodology loops-back to decision block  204  in FIG.  2 . 
     With renewed reference to FIG. 3, if the PC is not indicative of the R, T1 or T2 positions in decision block  300 , the methodology proceeds to decision block  312  where the PC is analyzed. If the PC is indicative of the P, N1 or N2 positions, the methodology advances to block  316  where the methodology selects N as SLPC. The methodology would then progress to bubble  216 . If the PC is not indicative of the P, N1 or N2 positions in decision block  312 , the methodology proceeds to decision block  320 . 
     At decision block  320 , the PC is analyzed. If the PC is indicative of the T3 or D positions, the methodology proceeds to block  324  where D is selected as SLPC. The methodology would then progress to bubble  216 . If the PC is not indicative of the T3 or D positions in decision block  320 , the methodology proceeds to decision block  328  where the methodology analyzes the PC. 
     If the PC is indicative of the T4 position in decision block  328 , the methodology proceeds to decision block  332  where SLP0 is analyzed. If SLP0 is R, N or D in decision block  332 , the methodology proceeds to block  324  and D is selected as SLPC. Operation of the SLP methodology in this manner essentially provides hysteresis for the D SLP position. If SLP0 is not R, N or D in decision block  332 , the methodology proceeds to block  336  where 2 is selected as SLPC. Operation of the SLP methodology in this manner provides hysteresis for the 2 SLP position. The methodology then proceeds to bubble  216 . 
     Returning to decision block  328 , if the PC is not indicative of the T4 position, the methodology proceeds to decision block  340  where the PC is analyzed. If the PC is indicative of the 2 position, the methodology proceeds to block  336 . Otherwise, the methodology proceeds to decision block  344 . 
     The PC is analyzed in decision block  344  and if it is not indicative of the T5 position, the methodology proceeds to decision block  348  where L is selected as SLPC. The methodology then proceeds to bubble  216 . If the PC is indicative of the T5 position in decision block  344 , the methodology proceeds to decision block  352  where SPL 0  is analyzed. If SLP0 is not L in decision block  352 , the methodology proceeds to block  336 . Operation of the SLP methodology in this manner provides hysteresis for the 2 SLP position. If SLP0 is L, the methodology proceeds to block  348 . Operation of the SLP methodology in this manner provides hysteresis for the L SLP position. 
     Branch B 
     With reference to FIG. 4, the methodology proceeds along branch B to decision block  400  where the PC is analyzed. If the PC is indicative of the R position, the methodology proceeds to block  402  where SLPC is set to R. The methodology proceeds to bubble  216  where subroutine B terminates. With brief reference to FIG. 2, the methodology then loops-back to decision block  204 . 
     Returning to decision block  400  in FIG. 4, if the PC is not indicative of the R position, the methodology proceeds to decision block  406  where the PC is analyzed. If the PC is indicative of the T1 or T2 positions in decision block  406 , the methodology proceeds to decision block  408  where SLP0 is evaluated. If SLP0 is R, the methodology proceeds to block  410  where the R-N subroutine is performed. The R-N subroutine utilizes pressure switch data to detect whether the manual valve  26  is being shifted out of the R position, allowing for improved response and performance of the SLP methodology. Additionally, the R-N guards against excessive slippage of clutches  34   b  and  34   d . Upon completion of the R-N subroutine, the methodology proceeds to proceeds to bubble  216  where branch B terminates. 
     Returning to decision block  408 , if SLP0 is not R, the methodology proceeds to decision block  412 . If SLP0 is N in decision block  412 , the methodology proceeds to block  416  where the N-R subroutine is performed. The N-R subroutine utilizes pressure switch data to detect whether the manual valve  26  is being shifted out of the N position into the R position, allowing for improved response and performance of the SLP methodology. Upon termination of the N-R subroutine, the methodology proceeds to bubble  216 . Returning to decision block  412 , if SLP0 is not N, the methodology proceeds to block  418  where SLPC is set to N. The methodology then proceeds to bubble  216 . 
     Referring back to decision block  406 , if the PC is not indicative of the T1 or T2 positions, the methodology proceeds to decision block  420  where the PC is evaluated. If the PC is indicative of the P, N1 or N2 positions in decision block  420 , the methodology proceeds to block  418 . If the PC is not indicative of the P, N1 or N2 positions in decision block  420 , the methodology proceeds to decision block  422 . 
     At decision block  422  the methodology determines if the PC is indicative of the T3 position. If the PC is indicative of the T3 position, the methodology proceeds to decision block  424  where SLP0 is evaluated. If SLP0 is R in decision block  424 , the methodology proceeds to block  418 . If SLP0 is not R in decision block  424 , the methodology proceeds to decision block  426  where the methodology determines if SLP0 is N. If SLP0 is N in decision block  426 , the methodology proceeds to block  428  where the N-D subroutine is performed. The N-D subroutine utilizes pressure switch data to detect whether the manual valve  26  is being shifted out of the N position into the D position, allowing for improved response and performance of the SLP methodology. Upon completion of the N-D subroutine, the methodology proceeds to bubble  216  where branch B terminates as described above. Returning to decision block  426 , if SLP0 is not N, the methodology proceeds to decision block  430  where SLP0 is evaluated. If SLP0 is D, the methodology proceeds to block  432  where the D-N subroutine is performed. The D-N subroutine utilizes pressure switch data to detect whether the manual valve  26  is being shifted out of the D position and into the N position, allowing for improved response and performance of the SLP methodology. Upon completion of the D-N subroutine, the methodology proceeds to bubble  216  where branch B terminates as described above. Returning to decision block  430 , if SLP0 is not D, the methodology proceeds to block  434  where SLPC is set to D. The methodology then proceeds to bubble  216  where branch B terminates as described above. 
     Referring back to decision block  422 , if the PC is not indicative of the T3 position, the methodology proceeds to decision block  436  where the PC is evaluated. If the PC is indicative of the D position in decision block  436 , the methodology proceeds to block  434 . If the PC is not indicative of the D position, in decision block  436 , the methodology proceeds to decision block  438 . 
     At decision block  438  the methodology determines if the PC is indicative of the T4 position. If the PC is indicative of the T4 position, the methodology proceeds to decision block  440  where SLP0 is evaluated. If SLP0 is R or N in decision block  440 , the methodology proceeds to block  434 . If SLP0 is not R or N in decision block  440 , the methodology proceeds to decision block  442  where the methodology determines if SLP0 is D. If SLP0 is D in decision block  442 , the methodology proceeds to decision block  447   a  where the orderly shut down (OSD) flag is checked. If the OSD flag is set in decision block  447   a , the methodology proceeds to block  444  where the D-2/2-D subroutine is performed. Under circumstances where SLP0 is D, the D-2/2-D subroutine utilizes pressure switch data to detect whether the manual valve  26  is being shifted out of the D position into the 2 position, allowing for improved response and performance of the SLP methodology. Upon completion of the D-2/2-D subroutine, the methodology proceeds to bubble  216  where branch B terminates. Returning to decision block  447   a , if the OSD flag is not set, the methodology proceeds to block  434 . 
     Referring back to decision block  442 , if SLP0 is not D, the methodology proceeds to decision block  446  where SLP0 is evaluated. If SLP0 is 2 indecision block  446 , the methodology proceeds to decision block  447   b  where the OSD flag is checked. If the OSD flag is set in decision block  447   b , the methodology proceeds to block  448  where the D-2/2-D subroutine is performed. Under circumstances where SLP0 is 2, the D-2/2-D subroutine utilizes pressure switch data to detect whether the manual valve  26  is being shifted out of the 2 position into the D position, allowing for improved response and performance of the SLP methodology. Upon completion of the D-2/2-D subroutine, the methodology proceeds to bubble  216  where branch B terminates. Returning to decision block  447   b , if the OSD flag is not set, the methodology proceeds to block  450  where SLPC is set to 2. 
     Referring back to decision block  446 , if SLP0 is not 2, the methodology proceeds to block  450  where SLPC is set to 2. The methodology then proceeds to bubble  216  where branch B terminates as described above. 
     Referring back to decision block  438 , if the PC is not indicative of the T4 position, the methodology proceeds to decision block  452  where the PC is evaluated. If the PC is indicative of the 2 position in decision block  452 , the methodology proceeds to block  450 . If the PC is not indicative of the D position in decision block  452 , the methodology proceeds to decision block  454 . 
     At block  454  the methodology evaluates the PC to determine if the PC is indicative of the T5 position. If the PC is not indicative of the T5 position, the methodology proceeds to block  456  where SLPC is set to L. The methodology then proceeds to bubble  216  where branch B terminates as described above. Returning to decision block  454 , if the PC is indicative of the T5 position, the methodology proceeds to decision block  458  where SLP0 is evaluated. If SLP0 is not equal to L in decision block  458 , the methodology proceeds to block  450 . If SLP0 is equal to L in decision block  458 , the methodology proceeds to block  456 . 
     Branch C 
     With reference to FIG. 5, the methodology proceeds along branch C to decision block  500  where the PC is analyzed. If the PC is indicative of the L position, the methodology proceeds to block  502  where SLPC is set to L. The methodology proceeds to bubble  216  where branch C terminates. With brief reference to FIG. 2, the methodology then loops-back to decision block  204 . 
     Returning to decision block  500  in FIG. 5, if the PC is not indicative of the L position, the methodology proceeds to decision block  506  where SLP0 is evaluated. If SLP0 is R in decision block  506 , the methodology proceeds to decision block  508  where the PC is evaluated. If the PC is indicative of the D or T4 positions in decision block  508 , the methodology proceeds to block  510  where SLPC is set to N. The methodology then proceeds to bubble  216 . Returning to decision block  508 , if the PC is not indicative of the D or T4 positions the methodology proceeds to decision block  512  where the PC is evaluated. If PC is indicative of the 2 position in decision block  512 , the methodology proceeds to block  514  where SLPC is set to D. The methodology then proceeds to bubble  216 . Returning to decision block  512 , if the PC is not indicative of the 2 position, the methodology proceeds to bubble  226  where the methodology advances to bubble  226  and enters branch D. 
     Referring back to decision block  506 , if SLP0 is not R, the methodology proceeds to decision block  518  where SLP0 is evaluated. If SLP0 is N, the methodology proceeds to decision block  520  where the PC is evaluated. If the PC is not indicative of the 2 position in decision block  520 , the methodology proceeds to bubble  226 . If the PC is indicative of the 2 position in decision block  520 , the methodology proceeds to block  522  where SLPC is set to D. The methodology then proceeds to bubble  216 . 
     Returning to decision block  518 , if SLP0 is not N, the methodology proceeds to decision block  524  where SLP0 is evaluated. If SLP0 is D, the methodology proceeds to decision block  526  where the PC is evaluated. If PC is indicative of the N1 position in decision block  526 , the methodology proceeds to block  528  where SLPC is set to N. The methodology then proceeds to bubble  216 . Returning to decision block  526 , if the PC is not indicative of the N1 position the methodology proceeds to bubble  226 . 
     Referring back to decision block  524 , if SLP0 is not D, the methodology proceeds to decision block  530  where the PC is evaluated. If the PC is indicative of the R, T2, N1 or N2 positions in decision block  530 , the methodology proceeds to block  532  where SLPC is set to N. The methodology then proceeds to bubble  216 . Returning to decision block  530 , if the PC is not indicative of the R, T2, N1 or N2 positions the methodology proceeds to decision block  534  where the PC is evaluated. If the PC is indicative of the T3 position in decision block  534 , the methodology proceeds to block  536  where SLPC is set to D. The methodology then proceeds to bubble  216 . 
     Returning to decision block  534 , if the PC is not indicative of the T3 position, the methodology proceeds to decision block  538  where SLP0 is evaluated. If SLP0 is 2 indecision block  538 , the methodology proceeds to bubble  226 . If SLP0 is not 2 indecision block  538 , the methodology proceeds to decision block  540  where the PC is evaluated. If the PC is not indicative of the D, T4 or 2 positions in decision block  540 , the methodology proceeds to bubble  226 . If the PC is indicative of the D, T4 or 2 positions in decision block  540 , the methodology proceeds to block  542  where SLPC is set to 2. The methodology then proceeds to bubble  216  where branch C terminates. 
     Branch D 
     With reference to FIG. 6, the methodology proceeds along branch D to decision block  600  where SLP0 is evaluated. If SLP0 is R, the methodology proceeds to block  410   a  where the R-N subroutine is performed. Upon completion of the R-N subroutine, the methodology proceeds to bubble  216  where branch D terminates. With brief reference to FIG. 2, the methodology then loops-back to decision block  204 . 
     Returning back to decision block  600  in FIG. 6, if SLP0 is not R, the methodology proceeds to decision block  604  where SLP0 is evaluated. If SLP0 is N, the methodology proceeds to block  416   a  where the N-R subroutine is performed. Upon completion of the N-R subroutine, the methodology proceeds to decision block  606  where SLPC is evaluated. If SLPC is not equal to SLP0 in decision block  606 , the methodology proceeds to bubble  216 . If SLPC is equal to SLP0 in decision block  606 , the methodology proceeds to block  428   a  where the N-D subroutine is performed. Upon completion of the N-D subroutine, the methodology proceeds to bubble  216 . 
     Referring back to decision block  604 , if SLP0 is not N, the methodology proceeds to decision block  608  where SLP0 is evaluated. If SLP0 is D, the methodology proceeds to block  432   a  where the D-N subroutine is performed. Upon completion of the D-N subroutine, the methodology proceeds to decision block  612  where SLPC is evaluated. If SLPC is not equal to SLP0 in decision block  612 , the methodology proceeds to bubble  216 . If SLPC is equal to SLP0 in decision block  612 , the methodology proceeds to block  444   a  where the D-2/2-D subroutine is performed. Upon completion of the D-2/2-D subroutine, the methodology proceeds to bubble  216 . 
     Referring back to decision block  608 , if SLP0 is not D, the methodology proceeds to block  444   b  where the D-2/2-D subroutine is performed. Upon completion of the D-2/2-D subroutine, the methodology proceeds to decision block  618  where SLPC is evaluated. If SLPC is not equal to SLP0 in decision block  618 , the methodology proceeds to bubble  216 . If SLPC is equal to SLP0 in decision block  618 , the methodology proceeds to block  432   b  where the D-N subroutine is performed. Upon completion of the D-N subroutine, the methodology proceeds to bubble  216 . 
     R-N Subroutine 
     Referring now to FIG. 7, the R-N subroutine will be described in detail. The R-N subroutine is entered at bubble  700  and progresses to decision block  704  where the methodology evaluates the low reverse pressure (LRP) flag. The LRP flag is set (i.e., logical state is 1) when pressure switch  28   d  detects the presence of fluid above a predetermined pressure. If the LRP flag is set indicating that there is sufficient fluid pressure to activate pressure switch  28   d , the methodology proceeds to block  708  where SLPC is set to N. The methodology then proceeds to bubble  712  where the subroutine terminates. Returning to decision block  704 , if the LRP flag is not set, the methodology proceeds to decision block  716  where the methodology determines if the restricted reverse port (RRP) flag has been set. The RRP flag indicates whether manual valve  26  has been shifted to a point where the flow of fluid to clutch  34   b  and/or clutch  34   d  is restricted, thereby causing excessive slippage of their elements which may damage transmission  16 . The RRP flag is set, for example, under the following conditions: 
     INR flag is set, indicating that transmission  16  is operating in the “R” gear ratio; and 
     the PDE flag is not set; and 
     the PC is indicative of the T1 or T2 positions; and 
     the turbine speed of the torque converter  14  exceeds output speed of transmission by a predetermined speed variance (e.g., 200 r.p.m.), indicating that there is slippage between the elements of clutch  34   b  and/or clutch  34   d.    
     If the RRP flag has been set, the methodology proceeds to block  708  and continues on as described above. If the RRP flag has not been set, the methodology proceeds to block  720  where SLPC is set to SLP0. The methodology then proceeds to bubble  712  and terminates. 
     N-R Subroutine 
     With reference to FIG. 8, the N-R subroutine is entered at bubble  800  and proceeds to decision block  804  where the methodology checks the soft LR apply (SAF) flag. The SAF flag is used to designate whether clutch  34   d  is being gradually engaged by modulating the pressure of the fluid supplied to it. The SAF flag, therefore, is used to prevent the erroneous interpretation of data from pressure switches  28  during the modulation of fluid pressure to clutch  34   d.    
     If the SAF flag is set indicating that fluid pressure to clutch  34   d  is being modulated, the methodology will proceed to block  808  where SLPC is set to SLP0. The methodology will then proceed to block  812  where the N-R subroutine terminates. 
     Returning to decision block  804 , if the SAF flag is not set indicating that fluid pressure is not being modulated, the methodology will proceed to decision block  816  where the RRP flag is checked. The RRP flag is discussed in detail in the section describing the R-N subroutine, above. If the RRP flag has been set, the methodology proceeds to block  808  and progresses as described above. If the RRP flag has not been set, the methodology proceeds to decision block  820  where the value of the engine speed (Ne) is checked. 
     If Ne is not greater than or equal to 500 r.p.m. indicating that pump  22  is not able to produce sufficient fluid pressure to operate clutches  34 , the methodology proceeds to block  808  and progresses as described above. If Ne is greater than or equal to 500 r.p.m. indicating that pump  22  is able to produce sufficient fluid pressure, the methodology proceeds to decision block  824  where the pressure switch mask (PSM) is checked. The PSM is comprised of five bits, each of which may be a 0 or a 1. Each bit is indicative of the state of a given pressure switch  28  in hydraulic circuit  20 . The first through fifth bits correspond to pressure switches  28   d ,  28   e ,  28   c ,  28   f , and  28   a , respectively. A logical state of 0 indicates that a given pressure switch  28  has not sensed the presence of a fluid which exceeds a predetermined pressure. A logical state of 1 indicates that a given pressure switch  28  has sensed the presence of a fluid which exceeds a predetermined pressure. 
     If one or more of the first, fourth and fifth bits of the PSM are not equal to zero (i.e., fluid pressure above a predetermined pressure has been detected by one or more of pressure switches  28   d ,  28   f  and  28   a ), the methodology proceeds to block  808  and progresses as described above. If the first, fourth and fifth bits of the PSM are each equal to zero (i.e., fluid pressure above a predetermine pressure has not been detected by pressure switches  28   d ,  28   f  and  28   a ), the methodology proceeds to decision block  828  where the LRON flag time (LRNT) is checked. 
     The LRON flag is set in response to the request by any portion of the methodology to enable clutch  34   d . The LRNT tracks the amount of time which elapses while the LRON flag is set. If LRNT is greater than a first predetermined time value (λ1), the methodology proceeds to block  832  where SLPC is set to R. LRNT essentially allows for sufficient time for fluid to actuate pressure switch  28   d  and as such, may be dependent upon the temperature of the fluid in transmission  16 . In the example provided, λ1 may vary between 0.2 and 2.5 seconds according to the formula: λ1=2.5−(T/36) where T is the temperature of the fluid in transmission  16 . The methodology then proceeds to bubble  812  and the N-R subroutine terminates. Returning to decision block  828 , if LRNT is not greater than a predetermined value λ1, the methodology proceeds to decision block  836  where the methodology determines if LRNT has exceeded a second predetermined value. 
     In the example illustrated, second predetermined (λ2) time is set at 14 ms. If LRNT has not exceeded λ2, the methodology proceeds to block  808  and progresses as described above. If LRNT has exceeded λ2, the methodology proceeds to decision block  840  where the previous status of the LRP flag (LRPi) is evaluated. 
     If LRPi was set (i.e., LRPi=1), the methodology proceeds to block  832  and progresses as described above. If LRPi was not set, the methodology proceeds to block  808  and progresses as described above. 
     N-D Subroutine 
     With reference to FIG. 9, the N-D subroutine is entered at bubble  900  and proceeds to decision block  902  where the status of the manual valve port restriction (MPR) flag is checked. The MRP flag indicates whether manual valve  26  has been shifted to a point where the flow of fluid to any of the clutches  34  which may be cycled when the shift lever is placed in the “D” position is restricted, thereby causing excessive slippage of the elements of one or more clutches  34  that support the operation of the presently operating gear ratio. The MRP flag is set, for example, under the following conditions: 
     the PDE flag is not set; and 
     the PC is indicative of the T3 position; and 
     one of the following occurs 
     a. the LDP flag is set as a result of either 1) a persistent variance between the speed of the torque converter  14  turbine and the output shaft of transmission  16 ; or 2) a persistent loss of pressure as detected by a pressure switch  28  on a hydraulic conduit  24  which supplies fluid to a clutch  34  that supports the operation of a presently operating gear ratio; or 
     b. a SL 1  test is performed repetitively for a predetermined number of times, each time resulting in a change of the SLP from N to D when the PC is indicative of the T3 position; or 
     c. the clutch of torque converter  14  is repeatedly turned “off” in response to a slipping condition at clutch  34   d  caused by a loss of fluid pressure which resulted from the combined effects of the operation of the clutch of torque converter  14  and the positioning of manual valve  26 . 
     If the MPR flag is set, the methodology proceeds to block  904  where SLPC is set to SLP0. The methodology then proceeds to bubble  906  where the N-D subroutine terminates. 
     Referring back to decision block  902 , if the MPR flag is not set, the methodology proceeds to decision block  908  where the instantaneous volume (V4C) through valve  32 f is checked. If V4C is not less than a predetermined volume, the methodology proceeds to block  904 . In the preferred embodiment, the predetermined volume is 0.1 cubic inches. Returning to decision block  908 , if V4C is less than the predetermined volume indicating that a SLP1 test may be performed without concern that clutch  34   f  may still have residual pressure from operation of transmission  18  in the overdrive gear ratio that could result in the indication of pressure exceeding a predetermined pressure by pressure switch  28   f . The methodology then proceeds to decision block  910  where the data from the pressure switch  28   f  is checked. If the data from pressure switch  28   f  does not indicate the presence of fluid exceeding a predetermined pressure and the methodology proceeds to block  904 . If the data from pressure switch  28   f  indicates the presence of fluid having a pressure exceeding a predetermined pressure, the methodology proceeds to block  912  where SLPC is set to D. The methodology then proceeds to bubble  906  where the N-D subroutine terminates. 
     D-N Subroutine 
     With reference to FIG. 10, the D-N subroutine is entered through bubble  1000  and proceeds to decision block  1002  where the methodology determines whether a continuity test is in process. The continuity test is performed periodically on solenoids  30  to ensure that they are operating properly. If the continuity test is in process, control of solenoids  30  is not possible and the methodology advances to block  1004  where SLPC is set to SLP0. The methodology then proceeds to bubble  1006  where the D-N subroutine terminates. Returning to decision block  1002 , if the continuity test is not in progress, the methodology proceeds to decision block  1008 . 
     In decision block  1008 , the methodology determines if Ne is less than 500 r.p.m. If Ne is less than 500 r.p.m., the methodology proceeds to block  1004 . If Ne is not less than 500 r.p.m., the methodology proceeds to decision block  1010  where the methodology determines if the element overlap control (EOC) is active. EOC is used when a serious fault has occurred in transmission  16  or transmission controller  18 , causing transmission  16  to be operated in an open-loop manner on a “limp-home” basis. 
     If EOC is active in decision block  1010  indicating that the SLP methodology should not be utilized, the methodology proceeds to block  1004 . If EOC is not active in decision block  1010 , the methodology proceeds to decision block  1012 . 
     In decision block  1012 , if a shift is being performed, the methodology evaluates the status of the neutral-to-first shift (N−1) flag. The status of N−1 flag indicates whether a shift from the neutral gear ratio to the low gear ratio is in progress. If the N−1 flag is not set indicating that a neutral-to-low shift is not in progress, the methodology proceeds to block  1004 . If the N−1 flag is set in decision block  1012 , the methodology proceeds to decision block  1014  where the status of the no drive logic (NDL) flag is checked. The NDL flag indicates that a serious fault has occurred and that transmission controller is attempting to vent clutches  34  to lower the speed of vehicle  10  prior to the opening of valves  32   a  and  32   g . Valves  32   a  and  32   g  allow transmission  16  to be operated in the “R”, “N/P”, “D” and “2” gear ratios strictly through the manipulation of manual valve  26 . Accordingly, the reduction in the speed of vehicle  10  is necessary to ensure that the opening of valve  32   g  will not cause damage to engine  12  or transmission  16  through inadvertence of the vehicle operator. If the NDL flag is not set, the methodology proceeds to decision block  1016 . 
     In decision block  1016 , the methodology determines whether the PSM is set to 00000. If the PSM is set to 00000 indicating that pressure switches  28   d ,  28   e ,  28   c ,  28   f , and  28   a  have not detected fluid pressure in excess of a predetermined pressure, the methodology proceeds to decision block  1018 . If the PSM is not set to 00000 indicating that one or more of pressure switches  28   d ,  28   e ,  28   c ,  28   f , and  28   a  have detected the presence of fluid in excess of a predetermined pressure, the methodology proceeds to decision block  1030 . 
     In decision block  1018 , the methodology checks the status of the IN2 flag. The IN2 flag indicative of whether transmission  16  is operating in the “2” gear ratio as activated by clutches  34   a  and  34   e . If the IN2 flag is set indicating that transmission  16  is engaged in the “2” gear ratio, the methodology proceeds to block  1020  where SLPC is set to N. The methodology then proceeds to bubble  1006  where the D-N subroutine terminates. Returning to decision block  1018 , if the IN2 flag is not set indicating that transmission  16  is not operating in the “2” gear ratio, the methodology proceeds to decision block  1022  where the status of the IN2PRIME flag is checked. 
     The IN2PRIME flag is indicative of whether transmission  16  is operating in the “2 prime” gear ratio as activated by clutches  34   a  and  34   f . If the IN2PRIME flag is set in decision block  1022  indicating that transmission  16  is operating in the “2 prime” gear ratio, the methodology proceeds to block  1020 . If the IN2PRIME flag is not set in decision block  1022  indicating that transmission  16  is not operating in the “2 prime” gear ratio, the methodology proceeds to decision block  1024  where the status of the IN3 flag is checked. 
     The IN3 flag is indicative of whether transmission  16  is operating in the “direct” gear ratio as activated by clutches  34   a  and  34   c . If the IN3 flag is set in decision block  1024  indicating that transmission  16  is operating in the “direct” gear ratio, the methodology proceeds to block  1020 . If the IN3 flag is not set in decision block  1024  indicating that transmission  16  is not operating in the “direct” gear ratio, the methodology proceeds to decision block  1026  where the status of the IN4 flag is checked. 
     The IN4 flag is indicative of whether transmission  16  is operating in the “overdrive” gear ratio as activated by clutches  34   c  and  34   f . If the IN4 flag is set in decision block  1026  indicating that transmission  16  is operating in the “overdrive” gear ratio, the methodology proceeds to block  1020 . If the IN4 flag is not set in decision block  1026  indicating that transmission  16  is operating in the “overdrive” gear ratio, the methodology proceeds to decision block  1028  where the status of the IN1 flag is checked. 
     The IN1 flag is indicative of whether transmission  16  is operating in the “L” gear ratio as operated by clutch  34   a  and occasionally  34   d , depending on the programming of the shift schedule. If the IN1 flag is not set in decision block  1028 , the methodology proceeds to decision block  1030 . If the IN1 flag is set in decision block  1028 , the methodology proceeds to decision block  1032  where the value of LRNT is checked. If the value of LRNT is greater than λ1, the methodology proceeds to block  1020 . If the value of LRNT is not greater than λ1, the methodology proceeds to decision block  1030 . 
     Referring back to decision block  1014 , if the NDL flag is set, the methodology proceeds to decision block  1030  where the value of PSM is checked. If the value of PSM is equal to 10000 indicating that only pressure switch  28   d  has sensed the presence of a fluid having a pressure in excess or a predetermined pressure, the methodology proceeds to decision block  1034  where the status of the PLU flag is checked. The PLU flag indicates that the torque converter  14  clutch is being used to control the slippage between the turbine and impeller of the torque converter  14  at or below a predetermined first maximum value. If the PLU flag is set, the methodology proceeds to block  1020 . If the PLU flag is not set in decision block  1034 , the methodology proceeds to decision block  1036 . 
     In decision block  1036  the methodology checks the status of the LU flag. The LU flag indicates that the torque converter  14  clutch is being used to control the slippage between the turbine and impeller of the torque converter  14  at or below a predetermined second maximum value which is generally less than the first maximum value used for PLU. If the LU flag is set, the methodology proceeds to block  1020 . If the LU flag is not set, the methodology proceeds to decision block  1038 . 
     Referring back to decision block  1030 , If the value of PSM is not equal to 10000 indicating that pressure switch  28   d  has not detected the presence of a fluid having a pressure which exceeds a predetermined pressure, the methodology proceeds to decision block  1038  where the value of PSM is checked. If the value of PSM is XXX00 indicating that pressure switches  28   f  and  28   a  have not detected the presence of a fluid having a pressure which exceeds a predetermined pressure, the methodology proceeds to decision block  1040  where the SLP1 flag is checked. The SLP1 flag indicates that a SLP1 test is being performed wherein solenoid  30   f  is activated and pressure switch  28   f  is checked. If pressure switch  28   f  detects the presence of a fluid having a pressure which exceeds a predetermined pressure, the transmission is operating in one of the forward gear ratios (e.g., low, 2, direct, overdrive). If pressure switch  28   f  does not detect the presence of a fluid having a pressure which exceeds a predetermined pressure, the transmission may be operating in the “N” or “R” gear ratios. 
     If the SLP1 flag has not been set for a time that is equal to or greater than a predetermined SLP1 test time (τ1), the methodology proceeds to decision block  1046 . Preferably, τ1 varies with the temperature of the fluid in transmission  16 . In the example illustrated, τ1 varies between 0.15 and 0.8 seconds. If the SLP1 flag has been set for a time greater than or equal to τ1, the methodology proceeds to decision block  1042  where the status of the IN1 flag is checked. 
     In decision block  1042 , if the IN1 flag is set, the methodology proceeds to block  1020 . If the IN1 flag is not set in decision block  1042 , the methodology proceeds to decision block  1044  where the N−1 flag is evaluated. If the N−1 flag is set in decision block  1044 , the methodology proceeds to block  1020 . If the N−1 flag is not set in decision block  1044 , the methodology proceeds to decision block  1046 . 
     Referring back to decision block  1038 , if the value of PSM is not XXX00 indicating that one or more of pressure switches  28   f  and  28   a  have sensed the presence of a fluid having a pressure which exceeds a predetermined pressure, the methodology proceeds to decision block  1046  where the methodology evaluates the INGEAR flag. The INGEAR flag is set whenever transmission  16  is not shifting between two gear ratios  16   a . If the INGEAR flag is not set, the methodology proceeds to block  1004 . If the INGEAR flag is set in decision block  1046 , the methodology proceeds to decision block  1048  where the status of the MPR flag is checked. 
     If the MPR flag is not set in decision block  1048 , the methodology proceeds to block  1004 . If the MPR flag is set in decision block  1048 , the methodology proceeds to decision block  1050  where the continuity of solenoids  30  are checked. If the continuity of solenoids  30  are not within a predetermined limit in decision block  1050  indicating that they may not be properly controlled, the methodology proceeds to block  1004 . If the continuity is within the predetermined limit in decision block  1050  indicating that solenoids  30  are controllable, the methodology proceeds to block  1020 . 
     D-2/2-D Subroutine 
     With reference to FIG. 11, the D-2/2-D subroutine is entered through bubble  1100  and proceeds to decision block  1102  where the methodology determines whether several “initial” conditions have been met. In the example provided, the “initial” conditions include: 
     fault counters for pressure switches  28   c  and  28   e  have a value of zero, indicating that these pressure switches are operational; and 
     the time since the previous SLP2 test has exceeded a predetermined time (λ3); and 
     the time since the last continuity test has exceeded a predetermined time (λ4); and 
     the last continuity test indicated proper continuity or the continuity failure (CFR) flag has not been set and solenoid  30   g  is operational; and 
     the transmission fluid temperature is greater than 15° F.; or SLPC is 2 or L; or the orderly shutdown (OSD) flag is set. 
     If the initial conditions are not met, the methodology proceeds to block  1116  where SLPC is set to SLP0. The methodology then proceeds to bubble  1128  where the D-2/2-D subroutine terminates. Returning to decision block  1102 , if the predetermined conditions have been met, the methodology proceeds to decision block  1104  where the methodology checks whether a set of “maintained” conditions have been met. In the example provided, the “maintained” conditions include: 
     Ne greater than 500 r.p.m.; and 
     the NDL flag is not set; or PSM not equal to 00000 and the INGEAR flag has been set for a time exceeding a predetermined time value τ2; and 
     the EOC flag has not been set; and 
     the D-2/2-D subroutine is requested. 
     If the “maintained” conditions have not been met, the methodology proceeds to block  1116 . If the “maintained” conditions have been met, the methodology proceeds to block  1106  where solenoid  30   g  is turned off, causing valve  32   g  to open. The methodology then proceeds to decision block  1108 . 
     In decision block  1108 , if the SLP2 flag has been set for a time that exceeds a predetermined SLP2 time (τ3), the methodology proceeds to block  1118  where the SLP2 test is terminated and solenoid  30   g  is turned on causing valve  32   g  to close. If the SLP2 flag has not been set for a time that exceeds τ3, the methodology proceeds to decision block  1110  where the methodology compares several pressure switch test masks: PSTMC, PSTM1, PSTM2 and PSTMi. Each pressure switch test mask includes two digits which may either be a 1 or a 0. The first and second digits of the pressure switch test mask are indicative of the data from pressure switches  28   e  and  28   c , respectively. A value of 1 indicates a logical state where the corresponding pressure switch has sensed the presence of a fluid having a pressure which exceeds a predetermined pressure. A value of 0 indicates a logical state where the corresponding pressure switch has not sensed the presence of fluid having a pressure which exceeds a predetermined pressure. PSTMC is the current pressure switch mask. PSTMi is the initial pressure switch mask at the start of the SLP2. PSTM1 and PSTM2 are initially set to PSTMi and are updated to reflect the previous and second previous pressure switch masks respectively. 
     Returning to decision block  1110 , if PSTMC, PSTM1 and PSTM2 are equal and PSTM2 does not equal PSTMi, the methodology proceeds to block  1118 . If PSTMC, PSTM1 and PSTM2 are not equal or if PSTM2 equals PSTMi, the methodology proceeds to decision block  1112  where the methodology checks the “maintained” requirements mentioned above in decision block  1104 . If any of the “maintained” requirements are not met, the methodology proceeds to block  1114  where the SLP2 test is terminated and solenoid  30   g  is turned on and valve  32   g  is closed. The methodology then proceeds to block  1116 . Returning to decision block  1112 , if all of the “maintained” requirements are still met, the methodology loops-back to decision block  1108 . 
     Referring back to block  1118 , once the methodology has turned solenoid  30   g  on and terminated the SLP2 test, the methodology proceeds to decision block  1120  where the values of PSTMC, PSTM1, PSTM2 and PSTMi are compared. If the values of PSTMC, PSTM1, PSTM2 and PSTMi are equal, the methodology proceeds to block  1121  where the SLP2 complete and verified (SLP2V) flag is set. The methodology then proceeds to decision block  1122  where SLP0 and the IN2 flag are checked. If SLP0 is D and the IN2 flag is set, the methodology proceeds to block  1124  where SLPC is set to 2. The methodology then proceeds to bubble  1128 . If SLP0 is not D or the IN2 flag is not set in decision block  1122 , the methodology proceeds to decision block  1130  where SLP0 and the IN3 and IN4 flags are checked. If SLP0 is 2 or L and either one of the IN3 and IN4 flags have been set, the methodology proceeds to decision block  1132  where SLPC is set to D. The methodology then proceeds to bubble  1128 . 
     Returning to decision block  1130 , if SLP0 is not 2 or L and/or if neither one of the IN3 and IN4 flags have been set, the methodology proceeds to block  1134  where SLPC is set to SLP0. The methodology then proceeds to bubble  1128 . 
     Referring back to decision block  1120 , if the values of PSTMC, PSTM1, PSTM2 and PSTMi are not equal, the methodology proceeds to decision block  1136  where the value of PSTMC and the status of the IN1 and IN2PRIME flags are checked. If the value of PSTMC is equal to 10 and the IN1 and IN2PRIME flags have been set, the methodology proceeds to block  1138  where SLPC is set to 2 and the SLP2 complete and verified (SLP2V) flag is set. The methodology the proceeds to bubble  1128 . Returning to decision block  1136 , if the value of PSTMC is not equal to 10 and/or if either of the IN1 and IN2PRIME flags have not been set, the methodology proceeds to block  1140  where the value of PSTMC and the status of the IN3 and IN4 flags are checked. 
     In decision block  1140 , if the value of PSTMC is equal to 11 and one of the IN3 and IN4 flags are set, the methodology proceeds to block  1138 . If the value of PSTMC is not equal to 11 and/or neither of the IN3 and IN4 flags are set, the methodology proceeds to decision block  1142  where the value of PSTMC and the status of the IN1 and IN2PRIME flags is checked. If the value of PSTMC is equal to 01 and the IN1 and IN2PRIME flags have been set, the methodology proceeds to block  1144  where SLPC is set to D and the SLPV flag is set. The methodology then proceeds to bubble  1128 . Returning to decision block  1142 , if the value of PSTMC is not equal to 01 and/or either of the IN1 and IN2PRIME flags have not been set, the methodology proceeds to decision block  1146  where the value of PSTMC and the status of IN2 are checked. If the value of PSTMC is 11 and the IN2 flag is set, the methodology proceeds to block  1144 . If the value of PSTMC is not 11 and/or the IN2 flag is not set, the methodology proceeds to block  1116 . 
     While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the description of the appended claims.