Encoder Interface

Model 427
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Features
4 quadrature encoder channels with 24-bit counters

5 MHz count rate

Individually loadable counters

Load-on-event and count-and-compare features

16 digital I/O lines with edge detection

Watchdog timer

Counters may be used as timers
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Description
Model 427 interfaces four incremental encoders to the ISA bus. Three flat cables connect the Model 427 to external breakout boards.

Encoders
The four 24-bit up/down counter channels are optimized for incremental encoders. Each channel accepts two phased TTL or RS-422 signals, plus an index signal. Unlike conventional counters, the 427 counters do not accumulate errors when the encoder dithers or changes direction.

Load-on-event - Each channel may be loaded with a preset count. The channels may also be programmed to load the preset count upon the occurrence of an index pulse, a terminal count, or a match count.

The 427 supplies 5-volt power to all encoder channels. Each counter can be programmed to function as an encoder interface or as a general-purpose timer and may optionally generate interrupts. To ensure maximum flexibility, no counter functions are used by any other onboard peripheral devices. The counters are double buffered to prevent data loss when reading accumulated counts.
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 Watchdog
The 427'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 427’s sixteen digital lines have standard pin-outs for solid-state relay boards. Each line is software programmable as an input or output. Inputs may be programmed for edge detection and interrupts. The status of output lines may be monitored by software. Whenever a system reset occurs all output channels are turned off.

Interrupts - each counter channel may be programmed to generate an interrupt upon  detecting an index pulse, a preset or terminal count.

Digital I/O lines programmed as inputs may generate interrupts when their state changes.
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Specifications
 General
Operating temperature -25C to +70C
PC bus interface I/O mapped, 64 ports
 Input power < 3 watts
Encoder I/O
Number of channels 4 quadrature
Length of counters 24 bits
Max count rate 5 MHz
Encoder counting 1x, 2x, 4x
Load preset count on events Index, terminal count
Overflow
Interrupt on events Index, count compare,
terminal count
Input voltage TTL or RS-422
Digital I/O
Number of I/O channels 16 bi-directional
Output voltage 0 to 5 VDC
Input sink current 100 mA, 1.1 volts

Watchdog Timer
Time-out: 800 mS seconds
2-pin connector may be connected to the bus reset line to allow a system reset from software.
Ordering information
Encoder accessories
4-channel encoder interface board 427
18" encoder cable, 26-pin 7503C
1 meter encoder cable, 26-pin 7503C1
Screw terminal board with DIN snap rails 7503TDIN
Digital I/O accessories
1 meter flat cable, 50 conductor 7501C1
24 position relay board w/DIN rails 720RB
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