Texas Instruments TMS3637P, Data Manual

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5–8
5.9 Transmitter Configurations
Of the total 31 data bits that are stored by the TMS3637, the last nine (CA through CI) configure the device
in one of 18 possible transmitter configurations. The device can run continuous, triggered, or
periodic in transmission. In addition, each of these functions can have a single, pulse, or train output in both
normal and modulated configurations. (For a definition of which configuration bits to set for all possible 18
transmitter configurations, see subsection 5.10.3.) To enter any transmitter configuration, always start by
setting EEPROM bits CA = 1 and CF = CG = CH = 0.
When OUT transmits the code, the code is considered to be inverted. OUT also requires an external pullup
resistor. When IN transmits the code, the code is the complement of OUT and is considered noninverted.
An internal pullup resistor is connected to IN, so no external pullup is required when it transmits the code.
5.9.1 Continuous Transmitter (CC = 1)
When the device is configured as a transmitter (CA = 1, CF = CG = CH = 0) and the EEPROM bit CC is set
to 1, the chip is programmed to function as a continuous transmitter. In this condition, the TMS3637 serially
transmits the same code indefinitely. The transmit sequence is enabled by setting TIME to low. TIME is
externally connected to a pullup resistor, so a simple switch between TIME and GND can force TIME low.
The code transmission continues as long as TIME is kept low. When TIME returns to high, the transmission
of the code is completed and the transmitter is disabled. The oscillator is consequently inhibited, and the
power consumption is reduced to the standby value (13
µ
A). The time between two consecutive codes (tbc)
during the transmission is equal to 57 pulse durations (tbc = 57 t
w8
, see Figure 3–6). The continuous
transmitter must be operated in either the normal (CB = 1) or modulated (CB = 0) modes.
5.9.2 Triggered Transmitter (CC = 0, CI = 1)
When the chip is configured as a transmitter (CA = 1, CF = CG = CH = 0) and EEPROM bits CC and CI
low and high, respectively, the chip is programmed to work as a triggered transmitter. The TMS3637
transmits a single code or a code train when TIME is forced low, and then the device enters the standby
mode. In order to retransmit a code, TIME must be taken high (or opened) and then forced low again. The
triggered transmitter must be operated in either the normal (CB = 1) or modulated (CB = 0) modes.
5.9.3 Periodic Transmitter (CC = 0, CI = 0)
When the chip is configured as a transmitter (CA =1, CF = CG = CH = 0) and the EEPROM bits CC and CI
are cleared to 0, the chip is programmed to work as a periodic transmitter. In this case, the internal pullup
resistor on TIME is disconnected and TIME is externally connected to V
CC
through a parallel RC. The
TMS3637 transmits one code or a code train and goes into the standby mode. After a time equal to one RC
time constant, the TMS3637 is enabled and transmits the code again. The TMS3637 then enters the standby
mode and repeats the process. During the code transmission, the external capacitor is loaded by V
CC
.
During the standby mode, it is discharged through the resistor. The transmission cycle starts again when
the capacitor voltage falls below the trigger value of TIME. In this way, it is possible to obtain a very low
average value of I
CC
. Typically, it is possible to obtain I
CC
= 1.5
µ
A at a transmission frequency of 2 Hz. The
periodic transmitter must be operated in either the normal (CB = 1) or modulated (CB = 0) modes.
5.10 Transmitter Modes
In addition to the three transmitter configurations discussed previously, the TMS3637 transmitter can
operate in four modes: normal, continuous, triggered, and periodic. The following paragraphs describe the
configuration bit setting required to place the TMS3637 in each of the four modes.