Terminal protocols

Abstract: Protocols for communicating between a digital data pro­ cessing system and a terminal. The terminal permits specifica­ tion of attributes for characters, of fill characters and their attri­ butes, of keyboard bit maps, and of different modes of specify­ ing a group of shifted characters. The protocols include a pro­ tocol which takes another as an operand and specifies how the second protocol is to be executed, a protocol which resets the attributes of a string of characters, protocols for shifting fields to the left and right, and protocols for loading bit maps and checking their correctness, and a protocol for obtaining the at­ tribute of the character at the current cursor position. There is also disclosed a new form of terminal to data processing sys­ tem protocol.

Description: The present invention relates to terminals and other apparatus attached to data processing systems and more particularly to protocols used for communicating between a terminal and a data processing system. Digital data processing systems are frequently connected to data input or display devices by means of asynchronous links over which data is transmitted as a series of sequential codes. Communication between the input or display device and the digital data processing system is achieved by means of protocols, sequences of codes to which the devices or the data processing system respond in a predetermined fashion. Prior-art protocols have defined rather simple operations, for example, the display of a character or the movement of the cursor. While such operations did serve their purpose, some desirable operations could not be specified and others could be carried out only by means of a long and complex series of protocols. As interactive computing has become popular, the need for more powerful protocols has become apparent. Such protocols increase the productivity of programmers by decreasing the complexity of dealing with terminals, and they increase the efficiency of systems using them by decreasing the number of protocols which must be sent between the data processing system and the input or display device. From European Patent Application Publication 43,697 a data transmission of the videotex type in which coded information can be transmitted from a central information store to plurality of terminals is known in which the coded information includes groups of bits representing characters and groups of bits representing control codes. A character attribute can be represented by a display control code which is transmitted in association with a cursor backspace code. Thus, the display terminal receives a sequence of codes representing either characters to be displayed or control codes which, for example, include attribute codes and active position movement codes. When a control code representing an attribute is received or subsequently received codes representing characters to be displayed are displayed according to that attribute code until the next attribute code is received. In order to change the attributes of a sequence of a currently displayed characters to the current attribute it is required to firstly send a sequence of active position movement control codes from the computer of the central information source to position the cursor to the first such desired character and secondly resend the sequence of codes representing the desired sequence of currently displayed characters. Heavy traffic on the communication link between the central informations store and the displayed terminal is the result. The present invention relates to protocols for communication between a data processing system and devices attached thereto and more specifically to protocols used with a video display terminal. In the video display terminal in which the present invention is employed, each character displayed on the terminal has associated with it a settable attribute specifying the manner in which the character is to be displayed. The terminal is highly flexible in other regards as well: any character displayable on the terminal may be specified as the fill character, i.e., as the character used in the terminal to represent places where there are no other characters. Further, the terminal may employ three different ways of specifying whether a character should be shifted, and finally, the terminal employs bit maps to control the behavior of certain keys. The present invention includes protocols which permit the digital data processing system using the terminal to take advantage of the terminal's flexibility and protocols which simplify formerly-complex operations. Among the protocols are the following: a protocol which takes another protocol as an operand and specifies the manner in which the second protocol is to be executed. a protocol which resets the attributes of a sequence of characters to a current attribute. protocols which shift a sequence of characters to the left or the right one position and insert a specified character in the open position. protocols which load bit maps and confirm that the loaded bit map is correct. a protocol to which the terminal responds by returning the attribute associated with the character at the current cursor position. a new form of protocol for use in transferring information from the terminal to the data processing system. It is the object of the invention to provide an apparatus operable with protocols which can reset the attributes associated with a sequence of characters. This is achieved with the apparatus as set out in claim 1. Other objects and advantages of the present invention will be understood by those of ordinary skill in the art after referring to the detailed description of a preferred embodiment contained herein and to the drawings, wherein: Brief Description of Drawings Fig. 1 is a block diagram prepresentation of a data processing system including a terminal in which the present invention is employed. Fig. 2 is a detailed block diagram of the terminal of Fig. 1 Fig. 3 is a flow chart showing the main processing loop executed by the terminal of Fig. 2. Figs 4A and 4B are a flow chart showing a detail of the process character block of the flow chart of Fig. 3, and Fig. 5 is a diagram showing the rewrite attributes protocol and the variables used to implement it in a present embodiment. Description of a Preferred Embodiment The following discussion of a preferred embodiment of the present invention wilt begin with an overview of data processing systems using terminals, continue with a discussion of a terminal in which the present invention is embodied, proceed to a detailed presentation of how the terminal handles the codes it processes, and conclude with detailed discussions of the individual protocols. 1. Overview of a Data Processing System with Terminal: Figure 1 Figure 1 presents an overview of a data processing system using a terminal. The system has two major components, host system 101 and terminal 111. Host 101 and terminal 111 are connected by asynchronous link 109. Host 101 receives data from and provides data to terminal 111 via asynchronous link 109. Asynchronous link 109 transfers the data as a series of code sequences. In a present embodiment, each code sequence consists at least of a start bit, a sequence of code bits, and a stop bit. The code may contain 7 or 8 bits. Additionally, the code sequence may contain a parity bit and/or a second stop bit. The code sequences sent between host 101 and terminal 111 form protocols. Sequences sent from host 101 to terminal 111 make up host-terminal protocols. By means of these protocols, host 101 provides data to and controls operation of terminal 111. Sequences sent from terminal 111 to host 101 make up terminal-host protocols, by means of which terminal 111 provides data and status information to host 101. Host system 101 includes memory 107 for storing data, CPU 103 for processing data, and controller 105, which operates under control of CPU 103 to provide the protocols required to transfer data to terminal 111 and control operation of terminal 111. In other embodiments, controller 105 may be lacking and CPU 103 may directly provide protocols to terminal 111. Terminal 111 contains keyboard 115, for inputting data to terminal 111, and display 113, for displaying data input from keyboard 111 or received from host system 101. A typical interaction between host system 101 and terminal 111 is the following: Host system 101 first sends host-terminal protocols to terminal 111 placing terminal 111 into the proper condition to perform the desired operation. Host system 111 then sends protocols representing text characters to terminal 111. The text characters appear on display 113 in the manner specified by the protocols used to put terminal 111 into the desired condition. Host system 101 then sends a protocol which moves a cursor on display 113 to a position at which the user of terminal 111 is to provide input. The user then employs keyboard 115 to input data to terminal 111, which transmits terminal-to host protocols via asynchronous link 109 to host system 101. Host system 101 may respond to the input provided from the user in the manner just described, and the user may then provide further input as required by host system 101. In general, the terminal-host protocols specify text characters, but some protocols specify modifications in following characters and others return information concerning the status of the terminal. 2. A Terminal Responsive to Protocols of the Present Invention: Figure 2 Figure 2 presents a block diagram of a terminal 111 responsive to the protocols of the present invention. Operation of terminal 111 is controlled by microprocessor 201. In a present embodiment, microprocessor 201 is a Motorola MC68B00, manufactured by Motorola, Inc. In other embodiments, other microprocessors may be employed. Microprocessor 211 is connected via bus 215 to the remaining components of terminal 111 and can provide data to and receive data from these components via bus 215. The other components include memory and devices for sending, receiving, and displaying data. The memory includes the following: Display RAM (random access memory) 225 for storing codes of characters to be displayed on display 113. Attribute RAM 223 for storing attribute codes how the characters in display RAM 225 are to be displayed in display 113. Attributes in a present embodiment include blinking, reverse video, high intensity, and underlining. Program data RAM 231 for storing data used in internal operation of terminal 111. Program ROM (read only memory) 251, containing the programs executed by microprocessor 201 while controlling operation of terminal 111. The other devices are the following; Switches 253 are switches set by a user of terminal 111 to specify certain options; Host port 233 is connected to asynchronous link 109 and has two components: IO data port 235 for receiving data from and providing data to host 101 and control port 237 for receiving control signals from host 101 and other devices in terminal 213 and providing control signals to host 101 via link 109; Keyboard port 227 is connected to keyboard 115 and receives key codes from keyboard 115; Display controller 217 is connected to display 113 and controls operation of display 113. Microprocessor 201 can address RAMs 223, 225, and 231, ROM 251, and registers in host port 233, keyboard port 229, and display controller 217. The registers have the following contents: In control port 237, there are two pairs of registers, PIAD 249 and PIAC 247, and PIBD 245 and PIBC 243. The D register of each pair contains data used in conjunction with a control signal; the A register contains a control code. In I/O data port 235, there are two registers: ACIAC 241, which contains a control code, and ACIAD 239, which contains data received in or to be sent from I/O data port 235. In keyboard port 227, there is a single register, Keyst 229, which contains the keystroke last input to keyboard 115. In display controller 217, there are two registers, CRTA 221, which contains an address in display 113, and CRTD 219, which contains data to be displayed at that address. Microprocessor 201 can further address switches 253 and read the current settings of the switches. Any data addressable by microprocessor 201 may be read from its location into one of microprocessor 201's internal registers; if the data at a location is writable, data may be read from one of microprocessor 201's internal registers to the location. Programs for microprocessor 201 may further specify arithmetic and logical operations on data contained in its internal registers. The registers have the following contents: PC 213 contains the address of the instruction which microprocessor 201 is currently executing. SP 211 contains the location of the top of a data stack in program data RAM 231. X 209 contains an address used to calculate the address of data. A 207 and B 205 contain operands for use in arithmetic-logical operations. CC 203 contains bits indicating the internal condition of microprocessor 201 after certain operations. In addition to receiving and outputting data via bus 215. microprocessor 201 produces addresses and control signals for the devices connected to bus 215 and responds to interrupt requests from host port 233. The interrupt requests are generated by host port 233 when terminal 111 receives data or control signals from host system 101, when it receives a keystroke from keyboard 115, or when it must renew the display on display 113. When microprocessor 201 receives an interrupt request, it interrupts the execution of the program it is currently executing, saves the current contents of its registers on the stack, and executes interrupt routines 252 from program ROM 251; when the interrupt routines are finished, microprocessor 201 restores the saved state and resumes execution of the program it was executing when the interrupt occurred. Thus, under control of a program from program ROM 251, microprocessor 201 may fetch data from one device in terminal 111, perform an operation on it, and store the result of the operation in another device in terminal 111. When the data is values for the registers of control port 237, I/O data port 235, or display controller 217, these devices may respond by outputting data or control signals to host 101 or to display 113. 3. General Mode of Operation of Terminal 111: Figure 3 The flow chart of figure 3 shows the general mode of operation of terminal 111. The flow chart, as is generally the case with flow charts and descriptions of operations disclosed herein has been simplified to include only those operations relevant to the present invention. For example, all input-checking operations have been omitted from the flow charts and discussions. As shown in figure 3, when terminal 111 is turned on, microprocessor 201 executes the operations represented by block 303. In the course of these operations, microprocessor 201 checks the status of the components of terminal 111 and initializes RAMs 231, 225, and 223 and the registers in control port 237, I/O data port 239, and display controller 217 to the proper values for commencement of operation. Microprocessor 201 then begins executing a main processing loop. Execution of the loop continues until terminal 111 is turned off. Each time microprocessor 201 executes the loop, it examines an area in program data RAM 231 which is used as a queue for storing bytes of data to which terminal 111 must respond. In the following, that queue will be referred to as HostB. As represented in decision block 305 of figure 3, if HostB is not empty, microprocessor 201 executes blocks 307 and 309. As indicated in block 307, microprocessor 201 takes the byte at the head of HostB, copies it into a register in microprocessor 201 and from there to a variable in program data RAM 231 which we shall term Key, and updates the head pointer for HostB so that the next byte in the queue is now the head of the queue. The byte is then processed as required by the protocol which terminal 111 is currently executing. If HostB is empty, microprocessor 201 checks a second queue in program data RAM 231 which will be called in the following KeyB. KeyB contains keystrokes received from keyboard 115. As represented in decision block 311, if there is no data in KeyB, microprocessor 201 again checks whether there is data in HostB. If there is data, microprocessor 201 checks a variable in RAM 231 which indicates whether the terminal is in local mode or is transmitting characters to host 101. When the terminal is in local mode, it responds directly to input from keyboard 115 and does not transmit that input to host 101. Decision block 313 shows that in the former case, blocks 319 and 321 are executed. The operation represented by block 319 copies the code at the head of KeyB into register A 207 and updates the head pointer for KeyB so that the next byte in the queue is now the head. The operation represented by block 321 writes the value of register A 207 to the tail of HostB 321. Microprocessor 201 then returns to the beginning of the loop, and will consequently eventually process the code received from keyboard 115. If the terminal is not in local mode, blocks 315 and 317 are executed. The effect of those operations is to output the character received from the keyboard to host 101. After outputting the character, microprocessor 201 again returns to the beginning of the loop. Execution of the main loop is interrupted whenever input from host 101 arrives at I/O data port 235, a keystroke arrives in keyboard port 227 from keyboard 115, or display 113 must be refreshed. In each of these cases, the result of the occurrence is the production of an interrupt request signal. As previously mentioned, microprocessor 201 responds to the interrupt request signal by saving the state of its internal registers in the data stack in RAM 231 and executing an interrupt routine in interrupt routines 252. That routine examines the internal registers in the devices to determine which one caused the interrupt and why there was an interrupt. It then executes the proper routine in interrupt routines 252 for dealing with that type of interrupt. When the interrupt routine is finished, the saved state is restored and execution of the main processing loop continues. When the interrupt occurred because a code was received from host 101, the interrupt routine stores the code received in ACIAD 239 at the tail of HostB; in the case of 7-bit codes, the high bit of the byte stored in HostB is set to 0. When the interrupt occurred because a code was received from keyboard 115, the interrupt routine stores the code received in Keyst 229 at the tail of KeyB. as previously explained, execution of the main processing loop eventually results in the processing of the code in process code block 309. When the interrupt occurred because display 113 must be refreshed, microprocessor 201 executes a routine which outputs the contents of display RAM 225 and attribute RAM 223 to display controller 217. What actually appears on display 113 depends on the character code stored in display RAM 225, the attributes corresponding to the character in attribute RAM 223, and the character set which is currently being used in terminal 111. The manner in which a character code is received from host 101 and displayed on display 113 provides a general example of the operation of terminal 111. The character code arrives via asynchronous link 109 in I/O data port 235 and is stored in ACIAD 239. On arrival of the character code, I/O data port 235 generates an interrupt request. As a result of the interrupt request, microprocessor 201 executes an interrupt routine which places the character code at the tail of HostB. On return from the interrupt, microprocessor 201 continues executing the main loop, and eventually processes the character code. In this case, the only action to be taken is the display of the character on display 113, so the processing of block 309 is merely a matter of writing the character and its attributes to the proper locations in display RAM 225 and attribute RAM 223. When the main loop is next interrupted to refresh display 113, the contents of RAM 225 are displayed, and consequently, the character corresponding to the character code is displayed. 4. Processing Protocols in Terminal 111: Figure 4 As previously mentioned, data and control information are transferred between host 101 and terminal 111 in the form of protocols. In a present embodiment, the data and control information in a protocol forms a sequence of one or more 7 or 8 bit codes. Within a given protocol, all codes are either 7 or 8 bits. The codes are processed in the order in which they are received in terminal 111. The first code is interpreted as indicating what action the terminal is to perform. If there is more than one code, the remaining codes contain information needed to perform the action specified by the first code. When a protocol contains only a single code, terminal 111 simply receives the code and performs the action specified by the code. Examples of such single code protocols are the protocols for the displayable characters. Each protocol contains a single character code. As previously described, terminal 111 responds to the character code by displaying the specified character on display 113. When a protocol contains more than 1 code, terminal 111 receives the first code, performs whatever processing is required, and sets a variable in RAM 231 which will be called State herein to a value which indicates the kind of operation specified by the first code. Terminal 111 then receives the second code and processes it as required by the value of the code and the value of State. If there are further codes, the processing for each code will be governed by the value of the code and the value of State and will include setting State to a new value. When the last code is processed, State will be reset to 0. A detailed flowchart of protocol processing in a present embodiment is provided by figures 4A and 4B. The flowchart in these figures represents the processing which occurs in process code block 309 of the main processing loop represented by figure 3. The processing is performed in a subroutine, and consequently, processing begins with a JSR (jump to subroutine) instruction in the main loop (terminal 401). Microprocessor 201 executes a JSR instruction by saving the address of the instruction following the JSR on the data stack in RAM 231 and setting PC 213 to the address of the first instruction in the subroutine, so that the next instruction to be executed is the first instruction in the subroutine. The first step performed by microprocessor 201 under control of the subroutine is storing the byte of code currently being processed, contained in the variable Key, in register A 207 of microprocessor 201. Next, microprocessor 201 performs processing necessary to convert certain codes from 7 to 8 bits. As will be explained in more detail later, such codes are preceded by a conversion code. In a present embodiment, that code has the value 04. As may be seen from decision block 455 and block 459, microprocessor 201 responds to the conversion code by setting a variable called Sethb and executing a RTS instruction (terminal 461) which restores the state which was saved by the JSR instruction (terminal 401) so that the operation in the main loop following block 309 is performed. When the code following the conversion code is received, Sethb is not equal to 0, and as shown in decision block 455 and block 457, in that case, the eighth bit is set in A and in Key and Sethb is cleared. Microprocessor 201 next determines whether the variable State = 0 (decision block 407). If it does, the code in register A 207 is the first byte of a protocol. The first byte is either a control code or some other kind of character (most likely a printable character). As shown by decision block 425, if it is the former, microprocessor 201 sets the variable State (block 427) and does whatever processing is required for that control code; if it is the latter, microprocessor 201 determines whether it is printable (decision block 429) and stores the character and its attributes at the proper locations in display RAM 225 and attribute RAM 223 so that the character will be displayed on display 113 the next time display 113 is refreshed. The proper locations in RAMs 225 and 223 are determined from variables in RAM 231 which contain the current address in display RAM 225 and the current attributes. In a present embodiment, the address of the attributes in attribute RAM 223 for a given character in display RAM 225 is at a constant offset from the address of the character in display RAM 225, and consequently may be computed by adding the offset to the address of the character in display RAM 225. If the character is neither printable nor a control code, microprocessor 201 simply proceeds to block 432 (figure 4B). If State does not equal 0 (decision block 407), microprocessor 201 next determines whether State = 45 (decision block 409). In this case, what is being processed is the second byte of a repeat next protocol. As will be explained in detail later, that protocol specifies that a following protocol be repeated the number of times specified in the second byte of the repeat next protocol. If the second byte of a repeat next protocol is being processed, processor 201 sets the variable Rtime from the second byte so that the following protocol will be repeated the specified number of times and sets the variable Rflag to indicate that the protocol to be repeated is to be loaded into the variable ComB in RAM 231 (block 415). Then processor 201 executes a RTS instruction (terminal 417), which ends the processing in block 309. If what is being processed is not the second byte of a repeat next protocol, microprocessor 201 determines from the value of Rflag whether the code is part of a protocol which is being saved to be repeated as specified by the repeat next protocol (block 411). If it is, the unshifted code is again moved from the variable Key to register A 207 and from thence to the tail of the queue in ComB (block 413). Whether the code byte is stored in ComB or not, it is then processed as required by its value and the current value of State (block 423), i.e., as required by the protocol to which the code belongs. The next step is decision block 432 (figure 4B). If microprocessor 201 is not executing the repeat next protocol , it executes a Rts instruction (terminal 433), thereby ending execution of process code block 309. If it is executing the repeat next protocol and has already processed the second byte of that protocol as described above, it is either loading the protocol to be repeated into ComB or executing the protocol to be repeated from ComB (decision block 435). If microprocessor 201 is loading and State does not = 0 (decision block 440), bytes of the command remain to be fetched from HostB and microprocessor 201 executes an Rts instruction ending the execution of process code block 309 for the byte just processed (terminal 441). If State does = 0, all of the bytes of the protocol to be repeated have been received and the loading operation performed in block 413 is finished. In this case, microprocessor 201 sets the variable Rflag to indicate that the loaded protocol is now being repeated (block 434) and resets a pointer, called herein BuffP, which indicates the byte to be next read from ComB to point to the first byte of the loaded protocol. When that is done, microprocessor 201 loads the first byte from ComB into the variable Key and branches to block 407 (figure 4A). Thus, the next byte to be processed in process code block 409 will be the first byte in ComB. Continuing with decision block 443, if the protocol to be repeated is not being loaded, it is being repeated. In this case, if State = 0 (decision block 443), the current repetition is finished. At the end of each repetition, microprocessor 201 decrements the variable Rtime (block 445). If Rtime does not equal 0, more repetitions remain, so microprocessor 201 branches to block 437 to set up the next repetition. If Rtime does equal 0, all repetitions are finished, so microprocessor 201 clears the variable Rflag (block 449) and executes a return instruction, ending execution of process code block 309 (terminal 451). If State does not = 0 (decision block 443), the microprocessor increments BuffP to ComB to point to the next byte of the stored command, fetches that byte (block 439), and branches to decision block 407 (figure 4A). As previously pointed out, the byte fetched from ComB will be the next code to be processed. 5. Detailed Discussion of Certain Protocols In the following, certain protocols responded to or produced by Terminal 111 will be described in detail. A figure will show the form in a present embodiment of each protocol. Each description will explain the protocol's form, function, and implementation in a present embodiment. Code values used in a present embodiment will be given in hexidecimal notation. Host to terminal protocols will be described first and then terminal to host protocols. The Rewrite Attribute Protocol: Figure 5 The rewrite attribute protocol is used to change the attributes of a sequence of characters in disclay RAM 225 to a current attribute value. The protocol and the variables used for its implementation in a present embodiment are shown in figure 6. Rewrite attribute protocol 701 is made up of three bytes: ESC code 604; RWA code 703, which has the value X57 Count 705, which specifies the number of characters from the current address in display RAM 225 whose attributes are to be altered. In a present embodiment, rewrite attribute protocol 701 is implemented as follows: in response to ESC code 604, microprocessor 201 sets State to 1; in response to State = 1 and RWA code 703, microprocessor 201 sets State to 40. In response to that value of State and Count 705, microprocessor 201 sets up a loop by setting the variable Temp 713 to the value of Count 705, setting variable Wk7 715 to the value of CurAddr 629, which, as already described, contains the value of the current address in display RAM 225, and adding the constant used to derive addresses in attribute RAM 223 to the value in Wk7 715 to produce the address of the corresponding attribute in attribute RAM 223 and places that address in Wk9. The variable Atb 709 contains the current attribute. The microprocessor then enters the loop. First, it writes the value of Atb 709 to the address specified by Wk9 717, thereby setting the attribute at that address to the current attribute. Then it loads the addresses in Wk7 715 and Wk9 into register X 209, increments them, and returns them to Wk7 715. Finally, it decrements Temp 713. If Temp 713 does not equal 0, microprocessor 201 repeats the steps of the loop. The attributes of the number of characters specified in Count 705 are thereby changed to the current attribute. 6. Conclusion The foregoing disclosure has shown now a terminal may be constructed which responds to and produces a variety of new and useful protocols and how the protocols themselves may be implemented in a preferred embodiment. As will be clear to those skilled in the art, the specific forms of the implementations described herein are dependent on the characteristics of terminal 111. In other terminals, or terminals employing other kinds of microprocessors, other implementations of the protocols described herein are possible, as are protocols which are formally different from the ones described herein but which contain substantially the same information and are responded to in substantially the same fashion by terminal 111 or host 101. In particular, the specific values of codes and variables disclosed herein are specific to the described embodiment and are intended to be purely exemplary.

Claims: Apparatus, in a display device(111,113), for controlling the display of a plurality of characters each associated with an attribute defining how the associated character is to be displayed, said apparatus comprising: processing means (201), responsive to a first protocol from a digital computer system (101), for specifying a current attribute; and writable attribute association means (223), controlled by said processing means (201) and responsive to a plurality of second protocols from said digital computer system, each of said second protocols representing a character to be displayed, for associating said current attribute with each of said characters to be displayed; characterized by : said processing means (201), also being responsive to a rewrite attribute protocol (701) from said digital computer system (101), said rewrite attribute protocol specifying a sequence of characters, and for controlling said writeable attribute association means (223) to associate said current attribute with each character of the specified sequence of characters. Apparatus according to claim 1, characterized in that : said processing means (201) operates to specify a selected one of the currently displayed characters; said rewrite attribute protocol (701) includes a rewrite attribute code (703) and a number-of-characters specifier (705); and said processing means (201) responsive to the rewrite attribute protocol (701) controls the writable attribute association means (223) so that each character in the sequence of characters beginning with said selected character and continuing for the number of characters specified by the number-of-characters specifier is associated with the current attribute.

Inventors: PEIRENT RICHARD JAMES, PEIRENT, RICHARD JAMES
Applicants: WANG LABORATORIES, WANG LABORATORIES INC.
Application year: 1985
Main classification: G06F3
IPC codes: G06F13, G06F15, H04L29, G06F3