Agere Systems Inc.
229
Data Sheet
July 2001
T8302 Internet Protocol Telephone
Advanced RISC Machine (
ARM
)
17 Key and Lamp Controller (KLC)
(continued)
Table 202. Noscan Control Register
Table 203. Noscan Delay Interval Encoding
When a key is pressed, the KLC includes a debounce interval during which the beginning of an LED drive period is
executed before the key is located. After the key is located, the KLC must finish the suspended LED drive period.
This takes roughly 10 ms, that accounts for the difference in key depression and key release noscan intervals.
17.3.3 Key Scan Status Register
The KLC updates the
key scan status register
to indicate the current status of the key scan matrix. The KLC
samples the key matrix every 12.5 ms. When the KLC detects a key depression, it will wait for a 2.5 ms debounce
interval and then scan each row in its key matrix. When it locates the specific key depressed, it will place that key’s
row and column location into the
key scan status register
and set the key press bit to 1. The KLC will delay set-
ting the press bit to 1 until the following clock cycle to ensure that an asynchronous read from the microprocessor
will not read the press bit as 1 with an invalid code. After setting the
key scan status register
, the KLC will then
wait its programmed noscan interval, before acting on any changes during its sampling interval. After the noscan
interval has elapsed, the KLC will check that key once every 12.5 ms to determine if that key has been released.
When the KLC detects that the key is no longer depressed, it will reset the press bit to 0. The KLC will wait its pro-
grammed noscan interval again before it will act on any new key depressions found during its sampling interval.
Address 0xE000 D100
Bit #
Name
Bit #
31:8
31:8
RSVD
7
6:2
1
0
RESET
RSVD
Noscan interval bit 1
Noscan interval bit 0
Name
RSVD
RESET
Description
Reserved.
Reset bit.
7
If 1, the KLC will reset. The
KLC interrupt register
and the KLC interrupt
enable register are left unchanged.
If 0, then the KLC will start (or continue) operation.
Reserved.
NOSCAN INTERVAL Noscan interval.
The noscan interval of the KLC can be changed through bits
0 and 1 of the
KLC
control register
. These bits will be reset to 1 (for the
default interval) by a hardware reset.
6:2
1:0
RSVD
Bit 1
0
0
1
1
Bit 0
0
1
0
1
Key Depression Noscan Interval
60 ms
22.5 ms
35 ms
47.5 ms (default)
Key Release Noscan Interval
50 ms
12.5 ms
25 ms
37.5 ms (default)