HCS361 Datasheet, PDF (8/24 Pages) Microchip Technology – KEELOQ CODE HOPPING ENCODER

HCS361
3.5.6 DELM: DELAY MODE
If DELM = 1, delay transmission is enabled. A delayed
transmission is indicated by inverting the lower nibble of
the discrimination value. The delay mode is primarily for
compatibility with previous KEELOQ devices. If
DELM = 0, delay transmission is disabled (Table 3-3).
TABLE 3-3 TYPICAL DELAY TIMES
TXWAK FAST
0
0
0
1
1
0
1
1
Number of
Code Words
before Delay
Mode
28
56
28
56
Time Before
Delay Mode
(VPWM = 0)
≈ 2.8s
≈ 2.9s
≈ 2.6s
≈ 2.8s
3.5.7 TIMO: TIME-OUT
If TIMO = 1, the time-out is enabled. Time-out can be
used to terminate accidental continuous transmissions.
When time-out occurs, the PWM output is set low and
the LED is turned off. Current consumption will be
higher than in standby mode since current will flow
through the activated input resistors. This state can be
exited only after all inputs are taken low. TIMO = 0, will
enable continuous transmission (Table 3-4).
TABLE 3-4 TYPICAL TIME-OUT TIMES
TXWAK FAST
0
0
0
1
1
0
1
1
Maximum
Number of
Code Words
Transmitted
256
512
256
512
Time Before
Time-out
(VPWM = 0)
≈ 25.6s
≈ 27.2s
≈ 23.8s
≈ 25.4s
3.5.8 IND: INDEPENDENT MODE
The independent mode can be used where one
encoder is used to control two receivers. Two counters
(SYNC_A and SYNC_B) are used in independent
mode. As indicated in Table 3-7, function codes 1 to 7
use SYNC_A and 8 to 15 SYNC_B. The independent
mode also selects IR mode. In IR mode function codes
12 to 15 will use counter B. The PWM output signal is
modulated with a 40 kHz carrier. It must be pointed out
the 40 kHz is derived from the internal clock and will
therefore vary with the same percentage as the baud
rate. If IND = 0, SYNC_A is used for all function codes.
If IND = 1, independent mode is enabled and counters
for functions are used according to Table 3-7.
For IND = 1 and S[3:0] ≡ 0xC, 0xD, 0xE, 0xF, Basic
Pulse Width modulation becomes:
TABLE 3-5 IR MODULATION
TXWAK FAST
Basic Pulse
0
0
0
1
1
0
(400µs)
(16x)
Period = 25µs
(200µs)
(8x)
1
1
(100µs)
(8x)
3.5.9 USRA,B: USER BITS
User bits form part of the discrimination value. The user
bits together with the IND bit can be used to identify the
counter that is used in independent mode.
3.5.10 XSER: EXTENDED SERIAL NUMBER
If XSER = 1, the full 32-bit serial number [SER_1,
SER_0] is transmitted. If XSER = 0, the four most sig-
nificant bits of the serial number are substituted by
S[3:0] and is compatible with the HCS200/300/301.
3.5.11 TMPSD: TEMPORARY SEED
TRANSMISSION
The temporary seed transmission can be used to dis-
able learning after the transmitter has been used for a
programmable number of operations. This feature can
be used to implement very secure systems. After learn-
ing is disabled, the seed information cannot be
accessed even if physical access to the transmitter is
possible. If TMPSD = 1 the seed transmission will be
disabled after a number of code hopping transmissions.
The number of transmissions before seed transmission
is disabled, can be programmed by setting the synchro-
nization counter (SYNC_A or SYNC_B) to a value as
shown in Table 3-6.
TABLE 3-6
SYNCHRONOUS COUNTER
INITIALIZATION VALUES
Synchronous Counter
Values
0000H
0060H
0050H
0048H
Number of
Transmissions
128
64
32
16
DS40146C-page 8
Preliminary
© 1996 Microchip Technology Inc.