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M-series RS232 Programmers Manual
M-series RS232 Programmers Manual
7.1 RS232 Message Fields
All RS232 messages, whether they are transmitted to or from the Matrix Mixer, use the same message
format. Each RS232 message contains five fields.
All values are transmitted in hexadecimal format
e.g. 0Ah.
For an explanation of transmitting in hexadecimal, please refer to section 7.3.
RS232_START length (2 bytes, MSB first) data (1 - n by
7.0 RS232 Message Protocol
RS232 Message Fields
The fifth field is a one-byte acknowledgment field, which is sent by the device which receives the message.
The value of this field is either RS232_ACK (FCh), RS232_BUSY (FDh), or RS232_ERROR (FEh).
The fourth field is a one-byte checksum. The value of the checksum is the additive sum of the bytes in the
first three fields, modulo 256 (the least significant byte).
For example, if the data portion (3rd field) of a message is (2, 3, 2, 5, 239, 19, 136), the length field is (0,
7). The additive sum of the first three fields is (250 + 0 + 7 + 2 + 3 + 2 + 5 + 239 + 19 + 136) = 663 =
297h. The checksum is 663 modulo 256 = 151= 97h.
The checksum feature can be turned off when necessary by setting DIP switch #7 to the down position.
This is recommended to simplify programming when using Crestron or AMX controllers. See section 3.1.
The third field, the data field, holds the parameters of the message e.g.
(02h, 03h, 02h, 05h, F2h, 13h, 88h).
The second field is a 2-byte length, transmitted most significant byte first. The value of the length field is the
number of bytes in the third field, the data field e.g. (00h, 07h).
The first field of a message is
always
the RS232_START byte (FAh).
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