Datum Systems PSM-500L Manual do Utilizador descarregar pdf (Página 2)

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

Rev 0.93 12/12/10

B-2

control of the PSM-500 is covered in the main manual. This Appendix describes the protocol for control of

the modem by an external computer or controller connecting to either the rear panel DB9 Control Port or

the rear panel USB port.

The controlling computer may take many forms ranging from an handheld/portable USB capable device or

dedicated stand-alone processor to a personal computer or a larger mini or main-frame computer, and is

referred to here simply as a controller. The PSM-500 contains full software allowing it to be externally

controlled. Note however that no software is provided for the external controller, which is the responsibility

of the user.

The protocol described here contains “place holders” within the data structure in two types, “Reserved” and

“Future Expansion”. The reserved data structure elements are used by the factory for specialized testing

and calibration. The future expansion elements are spares and data needed for yet to be implemented

features. The expanded frequency control needed in L-Band IF type modems were once “future” items.

Setup For Remote Control

Before the PSM-500 can be externally controlled it must be set to operate in the proper remote control

mode via the front panel. Several parameters must be set as dictated by the control system to be used:

1. Modem Address (all control methods)

2. Control Interface as either RS-232 or RS-485 (Control Port, J6)

3. USB Enable (USB port only)

4. Bit Rate, Format (all control methods, separate entries for USB and Control Port)

– default and standard are 9600, N,8,1.

5. Remote Protocol (Control Port) – must be set to “Binary Packet”.

Front Panel setting of these parameters is available in the <Unit: USB> and <Unit: Remote> columns.

These parameters may also be set via the remote control port itself, but this is dangerous, as it will probably

result in loss of communications.

The RS-232 interface is only useful in a point to point control with one controller and one modem because

of the nature of RS-232. The 485 type interface allows multiple modems and controllers to be tied to the

same serial bus. The modem address insures that the modem only responds to messages intended for it.

The RS-485 interface on the modem is configured as a “4 wire” interface. That means that the transmit and

receive wire pairs are separate. This allows a controller to both talk and listen at the same time. If a “2

wire” configuration is desired, the transmit and receive pairs may be simply tied together external to the

modem. Care should be taken here to insure that the “A” or “-“ side of the transmit is tied to the “A” or “-“

of the receive, and the same for the “B” or “+” side.

Packet Protocol Basics

All remote control communications are formatted as “packets” of information. The packets contain a

“header” and a data or “payload” section. The header is more like a wrapper around the data and includes

flags, addresses, commands, control information and a data byte count at the front of the message and a

closing flag and checksum at the end. The data field can be 0 to approximately 180 bytes depending on the

particular packet. A zero data byte count is only used to request information.

The modem never initiates transmission of a packet on its own, it only responds to a request or command

packet from the controller. The sequence of events in this protocol is for the controller to send a command

packet to a particular addressed modem. The addressed modem reads the command packet and if valid

executes the command and sends back a response packet. A response is always returned unless:

a) The unit is improperly addressed, which causes the modem to never see the packet, or

b) The message is globally addressed to all modems, or

c) The message flags or checksum are incorrect causing the modem to reject the message.

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

Comentários a estes Manuais

Sem comentários

Datum Systems PSM-500L Manual do Utilizador Página 2

Comentários a estes Manuais

Manuais e produtos relacionados com Redes Datum Systems PSM-500L