Multifunction analog/digital I/O | Model 421

Model 421 Multifunction analog/digital I/O
  • 3 quadrature encoder channels with 16-bit counters
  • Four 12-bit D/A outputs
  • Eight 12-bit differential A/D inputs
  • Watchdog timer
  • 48 bidirectional digital signals for solid state relay boards

Model 421 is a legacy product and is not recommended for new designs. Legacy products are available but may have lead times up to 12 weeks and minimum order requirements. Use our Product Finder to find a comparable product or contact our Design Support Team.


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.

Model 421 Typical Application



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 instrumentation 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-25 to 70 °C
PC bus interfaceI/O mapped, 16 ports
Input power< 3 W
A/D converter
Conversion time20 µS
Number of channels8 differential
Input resistance100 MΩ
CMRR100 dB minimum
Maximum common mode voltage5 V
Resolution12 bits
Accuracy14 bits
Input ranges±10, ±5 V
Offset error±1/2 LSB
D/A converter
Conversion time200 µs
Resolution12 bits
Offset error±2 LSB
Output voltage±10 V
Output resistance87 Ω
Digital I/O
Number of channels48 bi-directional
Output voltage0 to 5 V, open collector
Output sink current100 mA (at 1.1 V)
Encoder I/O
Number of channels3 quadrature, 16 bit
Input voltageTTL or RS-422
Input frequency350 kHz
Watchdog timer time-outTime-out: 500 ms
2-pin connector may be connected to the bus reset line to allow a system reset from software


File Version Type Size
Model 421 Instruction Manual1.0.0PDF93 KB


File Version Type Size
Model 421 DLL for Windows1.0.0ZIP76 KB
Other Operating Systems
Need a software development kit for another operating system? We can port our SDK to
your OS or provide the information you need to do it yourself. Contact Sales for details.

Pricing & Ordering

Model Description Qty 1 Qty 2-9 Order Qty.
421Multifunction analog/digital I/OCallCall 
Breakout Boards
7502TDINBreakout board, 20-pin, DIN rail mountable$53$53
7505TDINBreakout board, 50-pin, DIN rail mountable$87$79
7506TDINBreakout board, 40-pin, DIN rail mountable$85$78
Termination Boards
7409TBBreakout board, 40-pin, with temperature sensor$72$65
7409TCBreakout board, 40-pin, with temperature sensor and prototyping area$113$103
7409TDINBreakout Board, 40-pin, with temperature sensor and prototype area, DIN mountable$151$135
7409CCable, flat, 40 conductor, 18 inches$21$20
7409C1Cable, flat, 40 conductor, 1 meter$31$28
7501CCable, flat, 50 conductor, 18 inches$19$17
7501C1Cable, flat, 50 conductor, 1 meter$33$30
7502CCable, flat, 20 conductor, 18 inches$14$13
7502C1Cable, flat, 20 conductor, 1 meter$28$26

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