Analog & Digital Interface

Model 421

Model 421

Three quadrature encoder channels with 16-bit counters

Four 12-bit D/A outputs

Eight 12-bit differential A/D inputs, 50 kHz rate

Watchdog timer

Forty-eight bidirectional digital signals for solid state relay boards

PC/ISA compatible

The Sensoray Model 421 low cost interface saves space in ISA bus systems by combining five functions into one module. Four flat cables connect the Model 421 to external breakout boards.

Three 16-bit up/down counter channels are optimized for incremental encoders. Each channel accepts two phased TTL or RS-422 signals to track encoder direction and displacement. Unlike conventional counters, the 421 counters do not accumulate errors when the encoder dithers or changes direction. The 421 supplies 5-volt power to each encoder channel.

Eight differential input channels are multiplexed to a sample/hold and successive approximation A/D. A resistor-programmable instrumenta- tion amplifier allows gains of 1 to 1000. The 15-volt outputs from the DC/DC supply ensure A/D linearity for 10 volt input signals


Four voltage outputs channels may be programmed for 0 to +10 volts. One channel has a remote sense input to minimize line loss errors. All output voltages are reset to zero volts whenever a bus reset occurs.

The 421's watchdog timer output may be routed to either bus reset or nonmaskable interrupt. It may be enabled or disabled under program control. The timer is automatically disabled whenever a bus reset occurs

Digital I/O
The Model 421 has forty-eight digital I/O lines with industry standard pinouts for solid state relay boards. Each line is software programmable as an input or output. The status of output lines may be monitored by software. Whenever a system reset occurs all output channels are turned off.

Operating temperature -25C to +70C
PC bus interface I/O mapped, 16 ports
 Input power < 3 watts
 A/D Converter
Number of channels 8 differential
Input resistance 100 MW
 CMRR 100 dB min
Max common mode +5 volts
Conversion time 20mS
Resolution 12-bits
Input voltage range 0 to 10 V, +5 V
Offset error +1/2 LSB
D/A Converter
Conversion time 20mS
Resolution 12-bits
Offset error +2 LSB
Voltage output 0 to +10 volts
Output resistance 87W
Digital I/O
Number of channels  48 bidirectional
Output voltage 0 to +5 V open collector
 Output sink current 100 mA @ 1.1 V
Encoder I/O
Number of channels 3 quadrature, 16-bit
Input voltage TTLor RS-422
Input frequency 350 kHz
Ordering information
Analog I/O
18" analog cable, 40-pin 7409C
1 meter analog cable, 40-pin 7409C1
Low cost analog screw terminal board 7409TB
Screw terminal board with proto area 7409TC
Screw terminal board with proto area and DIN snap rails 7409TDIN
Digital I/O
18" digital cable, 50-pin 7501C
 1 meter digital cable, 50-pin 7501C1
 24 position relay board w/o DIN 720RB
 24 position relay board
 with DIN snap rails
18" encoder cable, 20-pin 7502C3
 1 meter encoder cable, 20-pin 7502C4
 Terminal board w/o DIN rails 7502TA
Screw terminal board with DIN snap rails 7502TDIN

Watchdog Timer
Time-out: 500 mS
 2-pin connector may be connected to the bus reset line to allow a system reset from software