Datum Systems PSM-500L Uživatelský manuál stáhnout pdf (Strana 3)

Datum Systems, Inc. PSM-500 Modem Remote Control Protocol

Rev 0.93 12/12/10

B-3

If the message packet address is accepted by the modem but the packet format is incorrect then an invalid

message response is returned. The response may take one of several formats depending on the command

type, but the response format for any particular command is fixed.

Example of Binary Packet Control System

An example Binary control system might consist of a single PC type computer communicating with one to

10 or more modems using an RS-485 interface card installed in the PC as one of the “Com” channels. This

setup might be used to monitor and control a small station. The PC could in turn be communicating with a

central computer system via a telephone line and modem. A program written in “C” or “BASIC” could

periodically request status of each modem to insure that nothing has changed, and upon command from the

central computer would change the parameters of any individual modem. For an example of the message

format similar to this, see the Binary Packet Command and Response Message sections below.

Binary Packet Command Message Format

The Binary Packet from the controller to the PSM-500 Modem adheres to the following message format.

Byte 0

Optional Pad

Byte FF hex

Byte 1

Opening Flag

A5 hex

Byte 2

Destination

Address 8 bits

Byte 3

Source

Address 8 bits

Byte 4

Binary Command

8 bits

Byte 5

Mode Byte

8 bits

Byte 6

Data Byte

Count

Byte 7 - (n-3)

Data Bytes

180 maximum

Byte n-2

Closing Flag

96 hex

Byte n -1

Checksum

Address Field

The modem is assigned an address via the front panel control or via the remote control line itself. Modems

are normally shipped with the address preset to “1”. When multiple modems are connected to the same RS-

485 control line each must have a unique address to avoid conflicts. A modem may have the same address

as any controller device on a shared bus (not recommended), but no two controller devices may have the

same address. Modems respond only to incoming messages containing their unique address in the

destination address position of the control message. A destination address of 255 (0xFF) is a global address

received by all modems.

The Source address may be any value from 0 to 254 that is not assigned to a modem and becomes the

destination address of the response message. This allows for multiple controllers in one system. The

convention of using 255 as the global address is assumed here also for controllers. The modem makes no

use of the source address other than to place it in the response packet directing the response to the

originating command source.

We tend to use controller addresses in the range 0xC0 to 0xCF, simply as an easy to remember mnemonic

for “Controller” 0 to 15.

When using the USB control port there are no addresses used or recognized in the packets in either

direction. This is because the USB protocols insure delivery to and from the proper destination.

Mode Byte Field

The Mode Byte is “05” for a local (near end) command, “06” hex for commands intended for the far end

(remote) modem. Access to remote modem requires that each modem be equipped with the Datum

Multiplexer and that it be enabled. Note that the mode byte is not returned in the response packet.

Command Byte Field

The Binary Command Byte is taken from the Command Tables below. Note that there may be multiple

command byte tables depending on the modem software version number. The software revision is read

from the front panel LCD display.

1 2 3 4 5 6 7 8 ... 56 57

Komentáře k této Příručce

Žádné komentáře

Datum Systems PSM-500L Uživatelský manuál Strana 3

Komentáře k této Příručce

Související produkty a manuály pro Sítě Datum Systems PSM-500L