
SSR-1U User’s Manual
Rev -, 27 Dec 2019
© 2019 Slerj, LLC
23
www.slerj.com
ACK messages have ID 0x90 with a single payload byte that is the message ID being
acknowledged. For example, an ACK for a Record message (ID=0x10) would comprise the
following:
Header
Payload
Checksum
Start1 Start2
ID
Count Payload Cksum1 Cksum2
0x81
0xA1
0x90
0x01
0x10
0xA1
0xC2
NACK responses to general messages have ID 0x91 and two payload bytes. The first payload
byte is the message ID that is being negatively acknowledged. The second payload byte
indicates the reason for the negative acknowledgement. For example, a NACK for a Record
message that was rejected because an invalid channel number (error code = 0x02) was specified
would be constructed as:
Header
Payload
Checksum
Start1 Start2
ID
Count
Payload
Cksum1 Cksum2
0x81
0xA1
0x91
0x02
0x10 0x02
0xA5
0x6C
For a list of error codes, see Section 5.4 Error Codes.
All general output messages (direction = out) must be polled by the user. A message is polled by
sending a message to the SSR-1U with the same message ID and zero payload. For example, to
poll the All Channel Status message (ID = 0x24), construct the poll message as follows:
Header
Checksum
Start1 Start2
ID
Count Cksum1 Cksum2
0x81
0xA1
0x24
0x00
0x24
0x48