Honeywell RS-232, Reference Manual

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Protocol Description
8/99 RS232 Communications Reference Manual 3
2. RS232 Port Protocol Description
2.1 Overview
This section of the manual describes the RS-232 “Configuration” port protocol for read/write access to
parameters in the UMC 800 Controller. It is intended for those not desiring to use the Microsoft Visual
C++ sample driver library provided and wish to use another programming language. The methods
described in the PC Communications Driver section along with the “peek & poke” utility file provided on
diskette may be used as a guide in driver development.
The protocol is loosely based on ANSI X3.28, utilizing asynchronous data transmission, DLE insertion for
data transparency prior to control characters, a two-byte CRC, and 32-bit 4-byte IEEE data formats. Data
Parameter access is via the function block number (1 through 249) and the index number of the parameter
within the block. Variables are addressed as block 250 with index numbers 0 through 149 (corresponding
to Variables 1 to 150).
The protocol allows for multiple parameter access in a read request message packet to increase data
throughput. This can be done by accessing a function block number and a contiguous range of parameter
indexes within that block or you may use a “scattered” message format to address multiple blocks and
indexes in any order. For the scattered message block method, up to 60 parameters may be read at once.
Writes are usually on a single block number, index basis but may also be on a multiple parameter basis
using the “scattered” message format (Maximum 40 or maximum packet size of 250 bytes). For instance,
this may apply to a range of Variables.
The link level data transmission format is to be fixed at 8 data bits, no parity, one stop bit and 9600 baud.
2.2 Definition of Error Types
Error Type Definition
Application The instrument rejected the message with an error code because the
request was invalid, bad sequence number, bad address.
Link Errors due to noise on the link, i.e. bad CRC.
Physical Errors which are trapped by the system or the hardware, i.e. timeout, bad
parity, bad framing.
2.3 DLE Insertion and Deletion
A DLE character will precede control characters. Any DLE that exists in the fields between the packet
header and footer will have an extra DLE inserted in front of it, which will be stripped out by the receiver,
similar to the zero insertion and deletion in HDLC protocol. On transmit, the CRC will be calculated before
DLE insertion is performed. On receive, DLE deletion will be performed before the CRC is checked.