Serial Interface Manual

Norbert Doerry
Last Update: July 5, 2004

1. Introduction

2. Using the Serial Interface Box

2.1 Power Connection

The Power Connection is a 2.1mm by 5.0 mm Male Power Jack. The interface requires 12 VDC Power. The center is positive, the outside negative (ground). The power switch is in series with with the positive connection. This 12V supply is converted to 5V internally to the interface and provided directly to the DIN-5 connectors on pin 5. The Power LED will be on to indicate that power is available to the unit.

2.2 RS-232 Interface

The Male DB-25 connector is configured as a DTE. This generally requires a cross-over cable when connected to a PC. The following pins are used:

Pin 2: TD (Output: Transmit Data)
Pin 3: RD (Input: Receive Data)
Pin 4: RTS (Output: Request to Send)
Pin 5: CTS (Input: Clear to Send)
Pin 7: Ground
Pin 20: DTR (Output: Data Terminal Ready)

RTS and DTR are both tied together and set "on"

Data will not be sent unless CTS is "on" (The CTS LED must be on)

The Baud Rate is set with an internal jumper to one of the following settings:

9600 (default)
4800
2400
1200
600
300

The communications parameters are hard wired for 1 start bit, 8 data bits, 1 stop bit, and no parity.

The data sample rate / periodicity for the Data Inputs is set with an internal jumper to one of the following settings:

18.8 Hz
9.4 Hz
4.7 Hz
2.3 Hz
1.2 Hz (default)
1.7 seconds
3.4 seconds
14 seconds

Data is sampled at the instance when the Clock LED on the indicator panel turns on.

2.3 5 Pin DIN Connectors

The standard pin-out for the 5 PIN DIN Connectors is:

Pin 1: Signal (or Control) A [Green]
Pin 2: Signal (or Control) B [Red]
Pin 3: Not Used (Reserved for Signal or Control C)
Pin 4: Ground [Black]
Pin 5: 12V [Yellow]

The order of the pins are clockwise (for the female connector) from the "key": 1,4,2,5,3

2.4 Input Ports

Up to 8 bits can be read into the serial interface. If a bit is left unterminated, it is read as a "1" by the interface. Shorting the input to ground will result in a "0" being read. The input lines are pulled up to 5 volts DC within the interface and directly feed an 74LS244 8-Bit Data buffer. External equipment should not drive this input higher than 5 volts. Most external equipment should interface to this device with relay contacts, 5 Volt TTL outputs, or open-collector NPN transitors.

There are 8 five-pin DIN connectors for the input ports. Pin one of each of the connectors is connected to the appropriate input on the serial interface. The Odd bits (D1, D3, D5, D7) are also connected to Pin 2 of the next lower connector (D0, D2, D4, D6 respectfully). In this way, one connector can provide input for 2 bits and only 4 connectors are needed for all 8 bits.

2.5 Output Ports

Up to 8 bits can be written from the serial interface. When a "1" is written, the corresponding output line is grounded via an Open-Collector output. When a "0" is written, the corresponding output line is in a high-impedance state. When the Serial Interface is powered up, all of the outputs are in a high-impedance state ("0").

As with the input ports, there are 8 five-pin DIN connectors for the output ports. Pin one of each of the connectors is connected to the appropriate output on the serial interface. The Odd bits (D1, D3, D5, D7) are also connected to Pin 2 of the next lower connector (D0, D2, D4, D6 respectfully). In this way, one connector can provide input for 2 bits and only 4 connectors are needed for all 8 bits.

Each of the output port bits can sink up to 300 ma of current when a "1" is written. In the high-impedance state (when a "0" is written), the output port can withstand up to 30 Volts DC. For more information see the data sheet for the 75451 Dual Peripheral Drivers.