2-181

Functional Pin Description

Table 4. Functional Pin Descriptions

Pin

Pin

Symbol

2000/2016 2020

Description

16

20

Power Supply

8

10

Ground

CLK

2

2

CLK is a Schmitt-trigger input for the external clock signal.

CHA

7

9

CHA and CHB are Schmitt-trigger inputs which accept the outputs

CHB

6

8

from a quadrature encoded source, such as incremental optical shaft

encoder. Two channels, A and B, nominally 90 degrees out of phase,

are required.

RST

5

7

This active low Schmitt-trigger input clears the internal position

counter and the position latch. It also resets the inhibit logic. RST is

asynchronous with respect to any other input signals.

OE

4

4

This CMOS active low input enables the tri-state output buffers. The

OE and SEL inputs are sampled by the internal inhibit logic on the

falling edge of the clock to control the loading of the internal position

data latch.

SEL

3

3

This CMOS input directly controls which data byte from the position

latch is enabled into the 8-bit tri-state output buffer. As in OE above,

SEL also controls the internal inhibit logic.

SEL

BYTE SELECTED

0

High

1

Low

16

A pulse is presented on this LSTTL-compatible output when the

quadrature decoder has detected a state transition.

U/D

5

This LSTTL-compatible output allows the user to determine whether

the IC is counting up or down and is intended to be used with the

15

A pulse is presented on this LSTTL-compatible output when the

HCTL-2020 internal counter overflows or underflows. The rising edge

on this waveform may be used to trigger an external counter.

D0

1

1

D1

15

19

D2

14

18

D3

13

17

D4

12

14

D5

11

13

D6

10

12

D7

9

11

NC

6

Not connected - this pin should be left floating.

These LSTTL-compatible tri-state outputs form an 8-bit output port

through which the contents of the 12/16-bit position latch may be read in

2 sequential bytes. The high byte, containing bits 8-15, is read first (on the

HCTL-2000, the most significant 4 bits of this byte are set to 0 internally).

The lower byte, bits 0-7, is read second.