Texas Instruments TMS3637P, Data Manual

Page: 35 / 53

6–3
R2
22 k
Ω
OSCR OSCC TIME GND
C1
10 nF
C2
0.1 nF
VCC IN CEX OUT
U1 (transmitter)
R8
22 k
Ω
OSCR OSCC TIME GND
C7
1 nF
VCC IN CEX OUT
U2 (receiver)
R6
22 k
Ω
R7
1 M
Ω
C5
470 nF
C4
680 pF
R5
100 k
Ω
R3
220
Ω
R4
100 k
Ω
R1
10 k
Ω
GND
VCC and Code
C6
10 nF
R9
220
Ω
D1
VCC
OUT
C3
47
µ
F
+
B
8 7 6 5
1 2 3 4 1 2 3 4
8 7 6 5
A
C
D
Figure 6–1. Two-Wire Direct Connection
6.2.2 Four-Wire Direct Connection
Table 6–2 lists the parts for the schematic of a four-wire direct connection of the transmitter/receiver shown
in Figure 6–2. In this example, the V
CC
, code, clock, and GND are provided through four separate wires.
The transmitter is configured as a normal continuous transmitter and the content of the configuration
EEPROM cells is:
CA CB CC CD CE CF CG CH CI
1 1 1 0 0 0 0 0 0
The transmitter uses its external oscillator to clock the data out. This external oscillator is a simple inverting
(NOT) gate that has a positive feedback loop through a resistor. The frequency of the oscillator is
approximately 26 kHz.
The receiver is configured as a logic normal (1-code) Q-state inverting receiver, and the content of the
EEPROM cells is:
CA CB CC CD CE CF CG CH CI
0 1 0 0 0 1 0 0 1
The receiver is used in the inverting mode. The code is considered to be inverted when using OUT on the
transmitter to transmit the code. The signal path between the transmitter and receiver does not invert the
signal; using the logic mode (CF = 1) also does not invert the signal. The result is a signal that is inverted
at the internal logic controller of the receiver; then use CI = 1, and an inverting receiver is used. (When IN
transmits the code, the signal is not inverted; then use CI = 0. An external pullup is not required when IN
is used in this manner).
As required, the oscillating frequency is approximately 260 kHz, which is a frequency approximately ten
times greater than that of the transmitter. This is provided by the internal oscillator in the receiver. OUT on
the receiver maintains the same status for approximately 0.5 seconds (1M
×
470 nF). A typical application
is an electronic key as shown in Figure 6–3.