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HP E1459A Register Definitions 85
Debounce Clock
Register Port 0 and
Port1/ Port 2 and
Port 3
The Debounce Clock Register (base + 1E
h
) can be read or written. This
register controls the clock rate to the debouncers. There are only two
programmable counters for all four ports. Port 0 and Port 1 share one
counter. This counter is controlled when bit 4 of the Control/Status Register
is "0". Port 2 and Port 3 share the other counter and are accessed when bit
4 of the Control/Status Register is "1". A 2
N
counter is used to generate the
clock, so times are binary powers. Table 3-1 shows the allowed values for
this register. This register is mirrored at address base + 2E
h
. Accessing
register base + 1E
h
is equivalent to base + 2E
h
. Programming the register to
0 is equivalent to programming it to 2, and programming it to 3 is the same
as 1.
Debounce Clock Register Port 0 and Port 1/Port 2 and Port 3 (base + 1Eh)
When BS = 0 in the Status/Control Register, the debounce clock for Port 0
and Port 1 are accessed. Port 0 and Port 1 use the same debounce clock.
With BS = 0 any value programmed into or read from this register will be
the same as the register at b + 2E
h
.
When BS = 1 in the Status/Control Register, the debounce clock for Port 2
and Port 3 are accessed. Port 2 and Port 3 use the same debounce clock.
With BS = 1 any value programmed into or read from this register will be
the same as the register at b + 2E
h
.
The following table lists the actual values for the debounce times:
b + 1E
h
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Write No Effect DEBOUNCE TIME
Read Always Returns FFF
h
0 0 0 DEBOUNCE TIME
Register Value Bit pattern (hex) Clock Frequency Clock Period Debounce Time
(4 - 4.5 clock periods)
2 (or 0, default) 0002
h
250 kHz 4 µS 16 - 18 µS
3 (or 1) 0003
h
125 kHz 8 µS 32 - 36 µS
4 0004
h
62.5 kHz 16 µS 64 - 72 µS
5 0005
h
31.25 kHz 32 µS 128 - 144 µS
6 0006
h
15.63 kHz 64 µS 256 - 288 µS
7 0007
h
7.81 kHz 128 µS 512 - 576 µS
8 0008
h
3.90 kHz 256 µS 1.0 - 1.13 mS
9 0009
h
1.95 kHz 512 µS 2.0 - 2.26 mS
10 000A
h
976 Hz 1 mS 4.1 - 4.6 mS
11 000B
h
488 Hz 2 mS 8.2 - 9.2 mS
12 000C
h
244 Hz 4.1 mS 16.4 - 18.4 mS
13 000D
h
122 Hz 8.2 mS 32.8 - 36.9 mS
14 000E
h
61 Hz 16.4 mS 65.5 - 73.8 mS