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GS-C200 Datasheet(PDF) 10 Page - STMicroelectronics |
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GS-C200 Datasheet(HTML) 10 Page - STMicroelectronics |
10 / 31 page The general format of a command string is the following: ADDRESS COMMAND ARGUMENT CHECKSUM CAR.RETURN The Address must be the first transmitted charac- ter and it is present only if the Multipoint protocol is used (at least one of SEL0, SEL1, SEL2 is different from zero). The Command is the second character(s) of the string, in the Multipoint protocol, but it becomes the transmission opening character when the Point-to- Point protocol is used (SEL0, SEL1 and SEL2 = 0). The Argument, if required, is specified immediately after the command and its length depends on the command type. The Checksum character verifies the correctness of the received string; its value is determined by the sum of the binary values of the preceding charac- ters. The result is cut at the seventh least significant bit and ORed with exadecimal 10 (C200S/C200 from V2.2) to make the result compatible with the transmission system. The last character, the string ending character, is always a Carriage Return that will be identified in the following by the symbol ( ↓). By connecting the pin CHS (pin 7) to ground, the checksum character is not anymore requested, and the task of guaranteeing the correctness of the message is left to the parity bit. It should be noted that by using this dialogue mode, the data integrity confidence level is reduced. Because motion sys- tems normally operate in manufacturing premises subjected to heavy electro-magnetic noise, and because any communication problem may have catastrophic effects on the system actions, it is a good practice to use the checksum character when- ever possible. The checksum character is normally not used (pin CHS connected to ground) when the GS-C is connected to a video-terminal, i.e. during the initial programming and debugging phase. In the following, three examples of command strings sent to a GS-C module are given. Example 1 - MULTIPOINT PROTOCOL. The Host Computer wants to set the USER output 3 of the module #2. The command will have the following format: 10/31 The checksum character 6 results from the binary sum of the character 2 (ASCII value = 32) + char- acter A (ASCII value = 41) + character 3 (ASCII value = 33) truncated at the seventh bit. Example 2 - POINT-TO-POINT PROTOCOL. The same instruction is given by the Host to a Point to Point connected module. The command will have the following format: A3t ↓ The checksum character has an ASCII value t that derives from the sum of the ASCII code A+3 = 41+33 = 74 in binary weighted code or t in ASCII code. Example 3 - POINT-TO-POINT PROTOCOL WITHOUT CHECKSUM. For the same instruction, the command format will be: A3 ↓ The string consists of command and argument only. The GS-C feeds back information to the Host every time it receives a command, therefore it has not to identify itself to the Host when answering in a Multipoint connection. The format of the string answered back by the GS-C is the following: ANSW.CODE ARGUMENT CHECKSUM CAR.RETURN The first character, which always identifies the an- swer type, may assume one of the following values: Y The command string has been correctly recei ved. B The controller is Busy and cannot process commands. R The controller is Ready to process commands. E An error has been detected. The type of error is specified by the number following the ”E”. V A controller status (a position or an USER input/output status) is sent back and its value is specified by the characters following the ”V”. The length of the Argument, present only for ”E” and ”V” answers, can range between 1 and 7 charac- ters, and it is a function of the received command. The number following the ”E” code, i.e. the error argument, specifies the detected error type accord- ing to the following table: 2A36 ↓ Address Module #2 Command Activate Argument USER out 3 Carriage return Checksum GS-C200 / GS-C200S |
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