Functional Pin Description
Table 4. Functional Pin Descriptions
Symbol
V
DD
V
SS
CLK
CHA
CHB
Pin
Pin
2000/2016 2020
16
8
2
7
6
20
10
2
9
8
Power Supply
Ground
CLK is a Schmitt-trigger input for the external clock signal.
CHA and CHB are Schmitt-trigger inputs which accept the outputs
from a quadrature encoded source, such as incremental optical shaft
encoder. Two channels, A and B, nominally 90 degrees out of phase,
are required.
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.
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.
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
0
1
CNT
DCDR
U/D
16
5
BYTE SELECTED
High
Low
MOTION SENSING
AND CONTROL
Description
RST
5
7
OE
4
4
SEL
3
3
A pulse is presented on this LSTTL-compatible output when the
quadrature decoder has detected a state transition.
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
CNT
DCDR
and CNT
CAS
outputs. The proper signal U (high level) or D
(low level) will be present before the rising edge of the CNT
DCDR
and
CNT
CAS
outputs.
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.
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.
CNT
CAS
15
D0
D1
D2
D3
D4
D5
D6
D7
NC
1
15
14
13
12
11
10
9
1
19
18
17
14
13
12
11
6
Not connected - this pin should be left floating.
2-181
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