Loopback; Figure 4-4 Loopback Request And Response Message Formats - Honeywell UMC800 Reference Manual

4.5 Loopback

Introduction
Figure 4-4 shows the Request and Response format for Function Code 250 - Loopback Test. This operation
lets you echo back a string of bytes from the controller to the Host.
Message Formats

Figure 4-4 Loopback Request and Response Message Formats

Request Message
READ/WRITE
0 = Read
FUNCTION CODE
250 = Loopback Test
NUMBER OF DATA BYTES WHICH FOLLOW
Response Message
ACKNOWLEDGE/
UNACKNOWLEDGE
09 = Acknowledge
0a = Unacknowledge
(See Table 2-1)
FUNCTION CODE
03 = Scattered 32 Bit Values
(If response is Unacknowledge, then an
error code is returned instead of a
function code. See Table 2-1.)
8/99
Header Byte 1 Byte 2
RS232 Communications Reference Manual
Byte 3
Byte 3+N
. . .
Data
Data
Nth BYTE OF DATA
1st BYTE OF DATA
. . .
Data
Data
1st BYTE OF DATA
NUMBER OF DATA BYTES WHICH FOLLOW
Message Exchange Formats
Nth BYTE OF DATA
31