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RS-232 Control of the AOR AR-2500

Interface Unit: None (connection is direct)

Standard Connections Used: TXD, RXD, GND (RTS/CTS also required with some models)

Type of RS-232 Command Set: ASCII text

AR-2500

This receiver is no longer in production and information about the RS-232 interface is no longer available, however, the details of the interface given here have been extracted from: Instruction Manual for Model AR2500 Turbo Scanning Monitor (1991).

I am not in a position to give assistance or further information on this radio since this is all I have.

The AR2500 RS-232 command interface is unusual in that it is text based but uses binary data fields. This means that simple operation using some of the commands is possible using a text-based terminal (such as MS-Windows Terminal), however, this is not possible for commands, such as frequency setting, which require data in the "pseudo-BCD" format (described below) that is used to represent frequency and mode information.

Port Parameters: 300, 1200 and 9600 baud with 8 bits, no parity and 1 stop bit.
Baud rate detection is automatic and relies on the computer sending a <CR> character repeatedly - when initialised, 'rS 232' appears on the receiver's display).

Flow control: hardware (RTS/CTS)
To prevent the receiver from experiencing data overflow, the CTS line is used by the receiver to inform the computer that it is prepared to receive data.

Type of interface: Mixed ASCII and "pseudo-BCD"

Signalling: To send data, the computer must first send a signalling character (such as a space) which is basically a request-to-send and is discarded. After the first signalling character is sent to the radio, the receiver responds by asserting CTS. This indicates to the computer that data can be sent.

Rear Panel Connector Pinout:

Memory Specific

The memories in the receiver are organised into 78 frequency banks (62 memory and 16 search). These are split into 62 scan banks with 32 frequencies per bank and 16 search banks with 2 frequencies per bank.

All frequencies are stored in descending order (for performance reasons). A 4-byte 'pseudo-BCD' format is used for the frequency data as follows:

MSD = most significant digit, LSD = least significant digit

FLAG specifies mode and step frequency data in the following format:

There can be up to 8 digits on the AR2500's front panel LCD display, however, two digits must be dropped from the BCD data. The lowest digit (0.5 kHz) can be dropped, since the firmware automatically detects when the AR2500 is in 12.5 kHz mode or when the frequency is a valid multiple of 12.5 kHz. The highest frequency value is 15000 kHz, so the two most significant digits can be represented in true BCD.

Example:

1250.9855, 12.5k/AM can be represented as:

The data is sent least significant byte first.

Command list

Most commands listed in the table directly emulate front panel operation from the keypad.

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This document maintained by simon.collings@cableinet.co.uk.
Material Copyright © 2000 Simon Collings