NEC PX-42VM3A User Manual - Page 46

Communication Format 8 bit 8 bit 8 bit 8 bit 8 bit 8 bit Command 1 Unit ID 1 Unit ID 2 Command 2 Data length Data Check sum 8 bit 8 bit Command 1 Command 1, along with command 2, is a number used to distinguish each command. In the case of ACK, when the lower order 4 bits is FH (as in 3FH and 7FH), this indicates that the commands and data of the supported equipment have been received. When the lower order 4 bits is BH (as in 3BH and 7BH), this indicates that unsupported commands and data have been received. Unit ID 1 and Unit ID 2 Unit ID 1 and unit ID 2 are numbers used to identify the equipment that is to be connected. 60H is used for the plasma monitor and 80H is used for external control equipment such as a personal computer. 1) Unit ID 1: Indicates the equipment sending the signal 2) Unit ID 2: Indicates the equipment receiving the signal Command 2 Command 2, along with command 1, is a number used to distinguish each command. Check Sum (CKS), Error Processing, and ACK 1) The check sum described below and RS-232C odd parity are used together for a check of the received data. The check sum is the lower order 8 bits of one frame of sent or received data comprising the sum total of Command 1, Unit ID 1 and 2, Command 2, Data Length, and Data. Check Sum Example DFH 80H 60H 47H 01H 01H Command 1 Unit ID 1 Unit ID 2 Command 2 Data Length Data Total 208H 08H Check Sum L 2) Error Processing • When the communication interval is vacant for more than 4 ms, thereafter a received Command 1 will be recognized. If, at this time, meaningful data cannot be recognized, that data will not be recognized (as valid data). • An ACK will not be returned unless the receive data error, the check sum error, and the receive data are all taken in. E-40