HCS300
4.3
Synchronous Transmission Mode
Synchronous Transmission mode can be used to clock
the code word out using an external clock.
To enter Synchronous Transmission mode, the Pro-
gramming mode start-up sequence must be executed
as shown in Figure 4-3. If either S1 or S0 is set on the
falling edge of S2 (or S3), the device enters Synchro-
nous Transmission mode. In this mode, it functions as
a normal transmitter, with the exception that the timing
of the PWM data string is controlled externally and 16
extra bits are transmitted at the end with the code word.
The button code will be the S0, S1 value at the falling
edge of S2 or S3. The timing of the PWM data string is
controlled by supplying a clock on S2 or S3 and should
not exceed 20 kHz. The code word is the same as in
PWM mode with 16 reserved bits at the end of the
word. The reserved bits can be ignored. When in Syn-
chronous Transmission mode S2 or S3 should not be
toggled until all internal processing has been com-
pleted as shown in Figure 4-4.
FIGURE 4-3:
SYNCHRONOUS TRANSMISSION MODE
t = 50ms
Preamble
Header
Data
T
PS
T
PH
1 T
PH
2
PWM
S2
S[1:0]
“01,10,11”
FIGURE 4-4:
CODE WORD ORGANIZATION (SYNCHRONOUS TRANSMISSION MODE)
Fixed Portion
Encrypted Portion
Serial Number
(28 bits)
Button
Status
S2 S1 S0 S3
DISC+ OVR
(12 bits)
Sync Counter
(16 bits)
LSb
Reserved
(16 bits)
MSb
Padding
(2 bits)
Button
Status
S2 S1 S0 S3
82 Data bits
Transmitted
LSb first.
©
2001 Microchip Technology Inc.
DS21137F-page 9
MICROCHIP [ MICROCHIP TECHNOLOGY ]
