Honeywell RS-232, Reference Manual

Page: 41 / 152

Message Exchange Formats
8/99 RS232 Communications Reference Manual 31
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
Header
READ/WRITE
0 = Read
FUNCTION CODE
250 = Loopback Test
NUMBER OF DATA BYTES WHICH FOLLOW
Byte 1 Byte 2 Byte 3
Request Message
Data
Byte 3+N
1st BYTE OF DATA
Nth BYTE OF DATA
Data
. . .
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.)
NUMBER OF DATA BYTES WHICH FOLLOW
Data
1st BYTE OF DATA
Data
. . .
Nth BYTE OF DATA