Dual processor architecture for electro generator

The present invention provides for an electro-surgical instrument with a rich graphical user interface (GUI) capability and a verifiable hardware and software platform meeting Food and Drug Administration (FDA) requirements. The rich GUI makes for a device which is more easily operated than prior art devices which lacked a sophisticated user interface. The increased functionality is achieved without sacrificing the ability to validate the device for FDA purposes. This goal is achieved by a dual processor design. In the dual processor design a control or master processor with verifiable source code implements the functions of: power delivery, temperature measurement, power measurement and power control. A display or slave processor, is functionally isolated from the first processor receiving only messages from the first processor. In a first embodiment of the invention an electro-surgical instrument is disclosed. The electro-surgical instrument includes a power delivery channel, at least one electrode and a display. The electro-surgical instrument also includes a control unit and a display unit. The control unit controls the operation of the power delivery channel and at least one electrode to deliver power to the surgical site. The control unit also determines at least one parameter of the power delivery channel and passing the parameter to the display unit. The display unit is coupled to the control unit and the display. The display unit accepts the at least one parameter, generates the graphical user interface on the display and displays the at least one parameter on the graphical user interface. In another embodiment of the invention a method for providing a graphical user interface in an electro-surgical instrument is disclosed.

SUMMARY OF THE INVENTION
 1. Field of the Invention
 This invention relates to the field of electro-surgical medical devices.
 More particularly, this invention relates to devices that deliver energy
 in the form of radio-frequency electrical current to tissue in order to
 perform surgical functions.
 2. Description of Related Art
 Various medical procedures rely on high-frequency electrical currents to
 deposit energy and thus heat human and animal tissues. During such
 procedures, a high-frequency current is passed through the tissue between
 electrodes. One electrode is located at the tip of a surgical probe.
 Another electrode is located elsewhere, and may be a ground pad or another
 surgical probe tip. The tissue to be treated lies between the electrodes.
 When the electrode circuit is energized, the electric potential of the
 electrodes at the probe tips oscillates at radio frequencies about a
 reference potential. If one is used, a ground pad remains at a floating
 reference potential. As the electric potential of the probe electrodes
 varies, a motive force on charged particles in the tissue is established
 that is proportional to the gradient of the electric potential. This
 electromotive force causes a net flow of electric charge, a current, to
 flow from one electrode, through the tissue, to any other electrode(s) at
 a lower potential. In the course of their flow, the charged particles
 collide with tissue molecules and atoms. This process acts to convert
 electrical energy to sensible heat in the tissue and is termed Joule
 heating.
 Upon heating, surgical functions such as cutting, cauterizing and tissue
 destruction can be accomplished. For example, tissues can be cut by
 heating and eventually vaporizing the tissue cell fluids. The vaporization
 causes the cell walls to rupture and the tissue to cleave. When it is
 beneficial to destroy tissue, comparatively higher rates of energy
 deposition can cause tissue ablation.
 Ablation of cellular tissues in situ is used in the treatment of many
 diseases and medical conditions either alone or combined with surgical
 removal procedures. Surgical ablation is often less traumatic than
 surgical removal procedures and may be the only alternative where other
 procedures are unsafe.
 The Food and Drug Administration (FDA) requires an extensive validation
 process for approval of radio frequency (RF) electro-surgical devices.
 This evaluation is designed to assure that any risks associated with this
 type of surgical procedures are minimized. The validation process requires
 documenting and testing all possible states and exceptions that can be
 generated by the combined hardware and software that makes up the RF
 Electro-Surgical device. Depending on the level of concern every line of
 source code must be documented to the satisfaction of the FDA. The degree
 to which computer controlled medical equipment is verified and validated
 depends on the level of concern. These levels of concern can also be
 applied to subsystems within a system. This latter requirement has
 prevented the introduction of complex graphical user interfaces (GUIs) for
 electro-surgical devices. Complex graphical user interfaces are certainly
 available on personal computers. These interfaces are generated using the
 proprietary software of companies such as Microsoft, e.g. Windows 95.RTM.
 and Apple Computer, e.g. System 7.RTM.. However, the source code for these
 well know operating systems is proprietary and thus can not be verified to
 the satisfaction of the FDA. Absent the use of these complex operating
 systems and development environments they provide, companies manufacturing
 electro-surgical devices have been limited in the complexity of their GUIs
 to those which can be generated with source code written in house.
 Typically electro-surgical device displays are limited to one or two lines
 of alphanumeric display without any graphical capability.
 What is needed is a way to create for electro-surgical instruments the more
 user-friendly GUIs found in Microsoft's or Apple's operating environments
 while staying in compliance with FDA guidelines for computer controlled
 surgical equipment.
 SUMMARY OF THE INVENTION
 The present invention provides for an electro-surgical instrument with a
 rich graphical user interface (GUI) capability and a verifiable hardware
 and software platform meeting Food and Drug Administration (FDA)
 requirements. The rich GUI makes for a device which is more easily
 operated than prior art devices which lacked a sophisticated user
 interface. The increased functionality is achieved without sacrificing the
 ability to validate the device for FDA purposes. This goal is achieved by
 a dual processor design. In the dual processor design a control or master
 processor with verifiable source code implements the functions of: power
 delivery, temperature measurement, power measurement and power control. A
 display or slave processor, is functionally isolated from the first
 processor receiving only messages from the first processor.
 In a first embodiment of the invention an electro-surgical instrument is
 disclosed. The electro-surgical instrument includes a power delivery
 channel, at least one electrode and a display. The electro-surgical
 instrument also includes a control unit and a display unit. The control
 unit controls the operation of the power delivery channel and at least one
 electrode to deliver power to the surgical site. The control unit also
 determines at least one parameter of the power delivery channel and
 passing the parameter to the display unit. The display unit is coupled to
 the control unit and the display. The display unit accepts the at least
 one parameter, generates the graphical user interface on the display and
 displays the at least one parameter on the graphical user interface.
 In another embodiment of the invention a method for providing a graphical
 user interface in an electro-surgical instrument is disclosed. The
 electro-surgical instrument includes a power delivery channel, at least
 one electrode and a display. The method for providing comprises the acts
 of:
 controlling with a control unit the operation of the power delivery channel
 and at least one electrode to deliver power to the surgical site;
 determining with the control unit at least one parameter of the power
 delivery channel;
 passing the at least one parameter from the control unit to a display unit;
 accepting at the display unit the at least one parameter; and
 displaying the at least one parameter on a graphical user interface
 generated by the display unit.

DETAILED DESCRIPTION
 The present invention provides for an electro-surgical instrument with a
 rich graphical user interface (GUI) capability and a verifiable hardware
 and software platform meeting Food and Drug Administration (FDA)
 requirements. The rich GUI makes for a device which is more easily
 operated than prior art devices which lacked a sophisticated user
 interface. The increased functionality is achieved without sacrificing the
 ability to validate the device for FDA purposes. This goal is achieved by
 a dual processor design. In the dual processor design a control or master
 processor with verifiable source code implements the functions of: power
 delivery, temperature measurement, power measurement and power control. A
 display or slave processor, is functionally isolated from the first
 processor receiving only messages from the first processor. These messages
 contain control parameters and data which allow the display processor to
 update the complex GUI's it displays during the course of a surgical
 operation. The display processor must respond to the control processor
 within a defined period of time. The display processor also verifies the
 data integrity by use of a cyclical redundancy check (CRC) algorithm. The
 GUI's are created in a complex operating environment which is proprietary
 and un-verifiable. That operating system can, for example, be Windows
 95.RTM. by Microsoft, or System 7.RTM., by Apple Computer.
 FIG. 1 shows an exterior isometric view of an embodiment of the
 electro-surgical generator. The electro-surgical generator includes a
 housing 100, an instrument 106, a ground pad 110 and a foot switch 104.
 The electro-surgical instrument 106 includes a probe 108, the tip of which
 may include one or more electrodes. The housing includes a color display
 120, a series of front panel parameter control buttons 122, a
 stand-by/ready button 126, a ready indicator light 124, an RF power
 delivery indicator light 128 and a fault indicator light 130.
 The housing contains both the RF delivery and control/master processor as
 well as the slave/display processor (see FIG. 2). The foot switch 104, the
 instrument 106 and the ground pad 110 are all coupled to the housing with
 flexible connectors.
 The electro-surgical device is placed in operation by user's activation of
 a power switch [not shown]. The surgical instrument 106 and specifically
 the probe portion 108 thereof is placed in contact with the patient at the
 appropriate surgical site. The probe may be delivered to the site directly
 through an opening or incision or may be guided to the surgical site
 through a catheter.
 After the appropriate diagnostics, the surgeon is able to move from the
 standby state in which operating parameters are entered, to the ready
 state in which parameters are set and power is not delivered to the
 instrument 106. The foot switch is also used to toggle the device between
 the ready and the operating state in which power is supplied to the
 surgical site. Details on the actual GUIs of an embodiment of the
 invention are displayed on display 120 (see FIGS. 8-9).
 FIG. 2 is a hardware block diagram of the dual processor design of the
 current invention. A power control and measurement unit 200 and a display
 unit 202 are shown. The power control and measurement unit 200 includes
 the control/master processor 204, a power delivery module 216, a power and
 impedance sensing circuit 214, temperature sensing circuit 212, the
 surgical instrument 106 as well as inputs from both the front panel
 control buttons 122,126 and the foot switch 104. The control processor 204
 interfaces with nonvolatile memory 220 and volatile memory 224. Memory 220
 includes the verified operating system 232 comprising in house source
 code. The memory 220 also includes control/target parameter file 236 and
 code for sending parameters 230A from the master processor 204 to the
 slave processor 206. The control parameter database contains operating
 parameters for a surgical procedure as a function of time. Thus a profile
 of temperature vs. time, power vs. time, and impedance vs. time is
 contained in this database, in this embodiment of the invention.
 The display unit 202 includes the display/slave processor 206, a keyboard
 208, a floppy drive 210 and the display 120 (see FIG. 1). The slave
 processor interfaces with memory 226. Memory 226 contains code for
 receiving parameters 230B at the slave processor from the master
 processor. Memory 226 also contains a proprietary operating system such as
 Windows 95.RTM. which is capable of supporting a complex GUI environment.
 The front panel buttons 122, 126 are direct connected to the control
 processor 204 as is the foot switch 104. These inputs allow the user to
 vary desired operating states of the system (see FIG. 3). The power
 delivery module 216 is coupled to the control processor 204, the surgical
 instrument 106 and to the power and impedance sensing circuit 214. The
 power and impedance measurement circuit is also coupled directly to the
 control processor. The temperature sensing circuit 212 is coupled to both
 the surgical instrument 106 and the control processor 204.
 A bidirectional bus to serial bus connects 240 connects the control
 processor 204 to the display unit 202 The display processor 202 is coupled
 to the keyboard 208, the floppy drive 210 and the display 120 (see FIG.
 1). The keyboard can be used to enter patient name and record so that that
 information along surgical history can be stored on a floppy disc.
 In operation the control processor 204 initiates the power-up and
 self-testing when a power-switch is enabled (not shown). After diagnostics
 have run the system is in standby mode and as such can accept adjustments
 by the surgeon to operating parameters such as time of operation and total
 energy. When the user transitions operation to ready mode by pressing the
 ready/standby button 126 the system enters ready mode. In ready mode the
 parameters are set. The system can then be moved to the operational mode
 using the foot switch 104. The control processor working with the control
 parameters stored in the control/target parameter file 236 or with user
 inputs from the front panel parameter control buttons 122 determines the
 appropriate control parameters for the operation from the control
 parameter code and the elapsed time since start of surgery. As the surgery
 progresses the power control and measurement unit 200 maintains the drive
 level of each RF channel at the level indicated in the control/target
 parameter file 236.
 For successive intervals throughout the operation new control parameters,
 e.g. target temperature or target power are downloaded to the power
 delivery module 216. The power delivery module 216 accepts from the
 power/impedance sensing circuit 214 an indication of the actual power
 delivered and compares that with the target power to calculate current and
 cumulative error. Then in an embodiment of the invention the power
 delivery module, using control algorithms such as proportional integral
 derivative (PID) adjusts the power delivery to the surgical instrument 106
 in a manner to minimize the difference between the actual power delivered
 to the surgical instrument and the target power to be delivered.
 An additional degree of safety is provided by sensors positioned in the
 surgical instrument 106 which allow temperature sensing circuit 212 to
 monitor the temperature of the tissue at the surgical site. If the
 temperatures exceed acceptable levels the control/master processor 204 may
 implement processes to abort power delivery. All of the above-mentioned
 processes take place independently of the display unit 202.
 The only communications passed between the power control and measurement
 unit 200 and the display unit 202 are messages 240A-B which will be
 described in greater detail in the following FIGS. 4-7. These messages are
 passed by program code for sending parameters 230A and by program code
 230B for receiving messages contained in respectively the memory of the
 control processor 204 and the display processor 206. Parameters such as
 total RF delivery time, impedance, power, energy, tip temperature, etc.
 are passed from the master control processor 204 to the display processor
 206 for display to the user on display 120 (see FIG. 1). The optional
 keyboard 208 allows the user to input new GUI interfaces and
 non-verifiable code into display memory 226. The floppy drive allows
 changes and/or additions to the non-verifiable program code 234 to be
 uploaded to the display processor. Neither the keyboard nor floppy drive
 provides an input path to the control processor 204 or more generally the
 power control and measurement unit 200.
 FIG. 3 is a process flow diagram of the major states for the verified
 operating system (OS) 232 in the power control and delivery module.
 Processing begins at process 300 in which a power-up reset operation is
 performed. After a power-up reset the control processor awaits the first
 acknowledge from the display processor indicating that the display
 processor is awake and ready to communicate. Control then passes to
 process 302 and 304 in which respectively a system self-test and a device
 self-test are performed. Various functions are performed such as testing
 of the various memories in the control processor, testing of the keyboard
 for stuck keys, measurement of various system temperatures, power supply
 voltages, and so forth, to ascertain the general health of the system. If
 a fatal fault is detected in either of these processes, control passes to
 process 314 in which the operation of the system is aborted. If a
 non-fatal fault in the device is detected control is passed to
 state/process 316. A non-fatal fault in the device might, for example,
 include a foot switch which was depressed or a surgical instrument 106
 which had not yet been connected to the housing 100 (see FIG. 1).
 Control then passes to state/process 306 when the system diagnostics have
 been successfully completed. In the stand-by phase global parameters are
 set to default or lowest values and additional user input to change these
 parameters is accepted from the front panel parameter control buttons 122
 (see FIG. 1). The user is thus able to increase or decrease parameters
 such as: total bum time, maximum impedance, maximum power, maximum energy,
 maximum temperature, total energy delivered, and total time of delivery.
 The user may also select the control/target parameter file 236 to be
 utilized by the surgical instrument to control the surgical procedure.
 The surgical device remains in the stand-by or idle state until the user
 enables ready/standby button 126 or the foot switch 104 to transition from
 the stand-by to the ready state 308 on the front of housing 100 (see FIG.
 1). The system is transitioned from the ready state 308 to the operational
 state 310 by the user's subsequent toggling of the foot switch 104 (see
 FIG. 1). Toggling of the foot switch moves the system back to the ready
 state 308 from the operational state. This assures that the system can be
 deactivated at any time without resetting the values of the control
 parameters to a default state. This allows the subsequent reactivation of
 the system.
 The user can change parameters such as maximum temperature, power, total
 procedure time and total energy delivery during either the stand-by or
 ready states, respectively 306-308. The user cannot change these same
 parameters while in the operational state 310. At the end of the total
 procedure time or the maximum energy end point, the system terminates
 operation and returns to the ready state 308.
 In the operational state, the power control and measurement unit 200
 operates within either user-defined parameters input with buttons 122 as
 well as those control parameter stored in the control/target parameter
 file 236. The control/master processor and the power delivery module 216
 monitor power and temperature delivered to the surgical instrument and
 adjust the power accordingly. The unit moves from the operational state to
 the ready state when the user toggles foot switch 104. The unit moves from
 the operational state to fatal fault state 314 when a fatal fault error is
 detected. Alternately, if in the operational state 310 an out of bounds
 condition is detected for impedance, control passes to impedance fault
 state process 312.
 In process 312 a determination is made as to whether impedance is outside
 an acceptable range. A high impedance might indicate that the surgical
 device has been removed from the surgical site. Alternately, if the
 impedance is too low there may be an equipment malfunction. In this event
 the control processor 204 returns the unit to either the stand-by state,
 the device fault state 316, the device self-test state 304, or the fatal
 fault state 314, depending on the nature of the fault.
 FIGS. 4A-B are process flow diagrams FIGS. 4A-B are process flow diagrams
 of the power delivery and measurement functions of the master processor
 204 (see FIG. 2). There are four primary subroutines dealing with
 respectively drive level error determination 450A, impedance error
 determination 452, drive level adjustment 450B and parameter passing 454.
 Subroutines 450A-B and 452 are implemented for each channel. All
 subroutines are sequentially engaged in throughout the course of the
 operational state 310 (see FIG. 3).
 Processing in the drive level error determination subroutine 450A begins
 with process 400. In process 400 a total elapsed time since the
 commencement of the operational state is updated and a corresponding power
 or temperature level is obtained by the control/master processor 204 from
 the control/target parameter file 236 (see FIG. 2). Control is then passed
 to process 402. In process 402 a wait state is introduced until the start
 of the next power and/or temperature sampling interval. At the start of
 that interval control is passed to process 404. In process 404 the power
 sensing circuit 214 (see FIG.2) measures the actual power delivered to the
 device during the sample interval. During that same interval the
 temperature sensing circuit 212 measures the temperature at the surgical
 site at which the probe of surgical instrument 106, e.g. the probe portion
 thereof (see FIG. 1) is positioned. Control is then passed to process 406.
 In process 406 the actual power and/or temperature level is compared with
 the targeted power and temperature profile discussed above in connection
 with process 400. The error for each of those parameters between the
 targeted value and the actual value is calculated. Control is then passed
 process 408. In process 408 an appropriate control law algorithm is
 applied to the error to calculate a new drive level which is stored for
 use in process 432 (see FIG. 4B). Control then passes to subroutine 452
 for the measurement of the impedance of the channel being measured.
 The impedance measurement is in a preferred embodiment of the invention
 distinct from the power measurement. They occur at different time interval
 within an overall cycle that transitions from impedance measurement to
 heating of the surgical site and then repeats itself. Additionally, if the
 impedance measurement interval for each channel is a fraction of the
 heating/power delivery interval for that channel the impact on the
 surgical site in terms of temperature rise, etc. is limited. No
 appreciable surgical activity, i.e. cauterizing, cutting, or ablation need
 take place during the impedance measurement. This has the advantage of
 allowing impedance measurements to be made at drive levels in excess of
 those utilized during the actual heating/power delivery interval (see
 process 432) which provides for a more accurate impedance determination by
 reducing the effects of background "noise".
 In still another embodiment of the invention, not only is the impedance
 measurement interval short, but it is also time division multiplexed (TDM)
 between the separate channels. High power levels are only applied for
 short intervals to a single channel at a time while the other channels are
 placed in a high impedance state. This avoids crosstalk between multiple
 electrodes that may be positioned on probe 108 thereby allowing for an
 accurate impedance measurement.
 Processing in subroutine 452 commences with process 410. In process 410 a
 wait state is introduced pending the start of the impedance measurement
 interval. Control then passes to process 412 at the start of the impedance
 measurement interval. In process 412 an elevated drive level appropriate
 for impedance measurement is downloaded by the CPU to the power delivery
 module 216 (see FIG. 2). This is 5 watts in this embodiment of the
 invention. Control is then passed to state/process 414 in which a wait
 state is introduced to the end of the impedance measurement interval.
 Control subsequently passes to process 416. In process 416, the impedance
 of the corresponding channel is calculated. Control then passes through
 splice block A to the continuation of subroutine 252 shown on FIG. 4B, and
 specifically decision process 430.
 In decision process 430, the control/master processor 204 using target
 impedance ranges contained in control/target parameter file 236 (see FIG.
 2) determines whether or not the measured impedance is out of a range. If
 the impedance is too low there may be an electrical malfunction. If the
 impedance is too high the electrode coupled to the channel may be coated
 with carbonated tissue, or the probe may have been removed from the
 surgical site. Control is then passed to process 312 (see FIG. 3), where a
 determination is made as to the cause of the out of range condition.
 Control is then passed to the appropriate state shown in FIG. 3. If,
 alternately impedance of the channel being measured is in range, control
 is passed to subroutine 450B.
 Adjustment of the desired drive level of each channel is accomplished in
 subroutine 450B. Processing begins at process 432. In process 432, a wait
 state is introduced for the beginning of the power/heating delivery
 interval. Control is then passed at the start of that interval to process
 434. In process 434, the drive level for the next heating interval
 calculated and stored above in connection with process 408 by the
 control/master processor 204 is downloaded to the power delivery module
 216 (see FIG. 2). That drive level is applied over the heating interval to
 the corresponding channel. Control then passes to subroutine 454.
 Parameter and data sending from the control/master processor 204 to the
 display processor 206 (see FIG. 2) is handled in subroutine 454.
 Processing begins at process 436 in which data and parameters to be passed
 to the display processor, e.g. power, temperature, and impedance for each
 channel are put in the payload portion of a message. Then a check is
 performed to assist the display processor in evaluating the integrity of
 the message it will receive. In an embodiment of the invention a cyclical
 redundancy calculation (CRC) is performed on the payload and added to the
 header of the message. Control is then passed to process 438. In process
 438, the message packet 240A is passed over by directional serial bus 240
 to the display processor 206 of the display unit 202 (see FIG. 2). Control
 is then passed to decision process 440. In decision process 440 the
 control processor waits for an acknowledge signal 240B from the
 display/slave processor 206 indicating that the package has been received
 and that the CRC calculated by the display processor for the package
 corresponds with the CRC calculated in process 422 above. If no such
 acknowledgment is received, control passes to process 314. In process 314
 (see FIG. 3) a fatal fault state is entered and the operation of the power
 control and measurement unit 200 is terminated. If alternately in decision
 process 426 an acknowledgment is received then control returns to the
 aforementioned process 400 (see FIG. 4A). The processing of each channel
 over the next impedance and heating intervals is then re-initiated.
 In this embodiment the entire cycle repeats once each second. The
 temperature sampling interval is coincident with the last 100 milliseconds
 of the power delivery or heating interval. The power delivery interval 432
 lasts for 900 milliseconds out of the one second cycle and the impedance
 measurement interval 410 is the 100 milliseconds of the 1 second cycle
 which is completely outside of the 900 milliseconds occupied by power
 delivery interval. The impedance measurement interval of each channel has
 a duration of 10 milliseconds for each channel.
 FIG. 5 is a process flow diagram for the processes associated with message
 passing as implemented on the display processor 206. Processing begins at
 decision process 500 in which a determination is made that the next
 message is received. If that determination is in the affirmative control
 passes to decision process 502. In decision process 502, the CRC for the
 message is independently calculated by the display processor and compared
 with the CRC in the header of the message as calculated by the
 master/control processor 204 (see FIG. 2). If the two do not match,
 control passes to process 504. In process 504, a NACK response 240B is
 sent from the display processor to the control processor 204. The display
 processor control then passes to process 314 in which the display
 processor enters the fault state (see FIG. 3). If alternately in decision
 process 502 the calculated CRC of the display processor and the control
 processor matches then control passes to process 508 and an acknowledge
 ACK is sent from the display processor 206 to the control processor 204
 (see FIG. 2). Control then passes to decision process 510.
 In decision process 510, a state field 612 (see FIG. 6A) is read in the
 message to determine whether the state has changed from, e.g. standby
 state 306, ready state 308, or operational state 310 (see FIG. 3). If an
 affirmative decision is reached i.e. that the state has changed then
 control is passed to process 512. In process 512, the display processor
 utilizing the receiving parameter 230B and display processes (see FIG. 2)
 refreshes the display 120 (see FIG. 1) with the appropriate graphical user
 interface for the new state. Control subsequently passes to decision
 process 514. Control also passes to decision process 514 from decision
 process 514 directly if there has been no state change.
 In decision process 514 a determination is made as to whether any of the
 parameters received in the message packet 240A have changed from their
 previous values. If a determination in the affirmative is reached then
 control passes to process 516. In process 516, the new parameters are
 updated for that portion of the graphical user interface in which
 parameters are listed (see FIGS. 8-9). Control then passes to decision
 process 518. Control also passes to decision process 518 directly if a
 negative determination is reached in decision process 514 i.e. that no
 parameter changes have taken place.
 In decision process 518 a determination is made as to whether any of the
 data, e.g. temperature and impedance, contained in the message has changed
 from previous values. If the determination is in the affirmative control
 is passed to process 520. In process 520, the updated parameters are
 written to the appropriate location of the GUI on the display 120 (see
 FIGS. 8-10). Control then returns to decision process 500 for the
 reception of the next message. If alternately in decision process 518 no
 data change is indicated in the message packet then control returns
 directly to decision process 500 for the detection of the next message.
 All the processes discussed above in connection with FIG. 5 are carried
 out by the display processor 206. The only message that the display
 processor can send to the control processor is the acknowledge ACK or the
 not acknowledge NACK.
 FIG. 6A shows the header portion 600 of a message and specifically the byte
 sequence 600A and the corresponding data 600B which the control/master
 processor 204 can send to the display processor 206 (see FIG. 2). FIG. 6B
 shows a table 602 with the various parameters 602A-B a message may
 contain. The parameter message is sent any time any parameter has changed
 and needs to be updated in the display processor. Reference 610 is the
 ASCII character that indicates that this message is a parameter message.
 Reference 612 is the field whose contents indicates what state the control
 processor was in when the message was sent. Possible states include:
 power-up reset, system self test, device self test, standby, ready,
 operational impedance fault, device fault or fatal fault. Reference 616 is
 the beginning of the cyclical redundancy check field in the message.
 Reference 614 is the parameter field, the contents of which are set forth
 in table 602A-B. The value immediately follows the parameter field. The
 types of parameters are target temperature 630, maximum power, end-point
 energy, end-point time or model select. By way of example, if the operator
 pressed the time end-point increment button while in the standby state,
 the following message would be sent. The field 610 would have the content
 "P" for parameter message. The state field 612 would have the content
 indicating a standby state. The field 614 would indicate that the
 parameter type is time end-point. The value low byte and high byte would
 have the actual time endpoint, and the cyclical redundancy check would be
 calculated for the message and put in field 616.
 FIG. 7 shows the structure of the payload 700 for a data message that the
 control processor can send to the display processor. The payload is shown
 with the byte sequence 700A and a corresponding parameter 700B for a data
 payload. The data message shown in reference 438 in FIG. 4B is being
 transmitted by the control processor and is being received by the display
 processor in reference 500 in FIG. 5. Reference 710 indicates that the
 message is a data message. Reference 712 indicates what state the control
 processor was in when the data message was sent and all the following
 fields in the data message are the current values of the data. For
 example, reference 714 is the most significant byte of the temperature for
 channel number 0.
 FIG. 8 shows the appearance of the standby GUI 800 generated by the display
 processor in the standby state 306 (see FIG. 3). Fields 814A-B show the
 total burn time, maximum impedance, maximum power, maximum energy, maximum
 tip temperature, maximum insulation temperature and total energy. The
 temperature is shown in field 802, the energy endpoint in field 804, the
 model selection for the surgical instrument in field 806, the ACK/NACK
 status in field 820, the maximum power in field 808 and the time endpoint
 in field 810. Anytime a message is sent from the control processor to the
 display processor while the control processor is in the standby state the
 display processor will go into the standby state and display the screen in
 FIG. 8.
 FIG. 9 shows the GUI 900 of the display processor in the ready state. As in
 the case of the standby screen in FIG. 8, these screens are shown when the
 display processor enters the corresponding state. For example, if the
 control processor was in the ready state when a message was sent it would
 put the display processor into the ready state by the state field 612 in
 the header of the message (see FIG. 6). In response the display processor
 would select the appropriate GUI and fill in the corresponding data and
 parameters. In the ready state fields 814A-B show the total burn time,
 maximum impedance, maximum power, maximum energy, maximum tip temperature,
 maximum insulation temperature and total energy. The temperature is shown
 in field 802, the energy endpoint in field 804, the model selection for
 the surgical instrument in field 806, the ACK/NACK status in field 820,
 the maximum power in field 808 and the time endpoint in field 810. In
 addition temperature samples 910 for each channel are displayed along with
 impedance samples 920. The data for these samples is contained in the
 payload of a ready message. Reference 920 shows the maximum impedance,
 meaning the highest impedance of any active channel, this information also
 having been obtained from the data message of FIG. 7.
 FIG. 10 shows the GUI 1000 of the display processor in the operational
 state. In the operational state fields 814A-B show the total bum time,
 maximum impedance, maximum power, maximum energy, maximum tip temperature,
 maximum insulation temperature and total energy. The temperature is shown
 in field 802, the energy endpoint in field 804, the model selection for
 the surgical instrument in field 806, the ACK/NACK status in field 820,
 the maximum power in field 808 and the time endpoint in field 810. In
 addition a graph 1002 of the temperature of each device tip as a function
 of time is displayed. These temperatures are also obtained from the data
 messages shown in FIG. 7.
 Although the foregoing invention has been described in detail for purposes
 of clarity of understanding, it will be obvious that certain modifications
 may be practiced within the scope of the appended claims.