TOIM3232

 Pulse shaping function (shortening and stretching) used in infrared IrDA standard applications
 Directly interfaces the infrared transceiver TFDS3000^*) to an RS232 port
 Programmable baud clock generator (1200 Hz ~ 115 kHz), 13 baud rates
 3 V and 5 V operation
 SO16L package

Figure 1 shows a typical example of a UART interface. As shown, XIN accepts the 1.8432 MHz input clock, and B_CLK accepts the 16 times baud rate clock.

Set S1 = S0 = LOW ("0"). When RESET = 0, the TOIM3000 sends the data to, or receives the data from the infrared transceiver TFDS3000. If Reset is active, RESET = 1, the TOIM3000 handles the normal electrical data exchange with the RS232 port. R1 = 2.2 k
optional (only necessary when RxDRD IR
line is capacitive loaded).

R2 = 100
, R3 = 10
, C1 = 6.8 F and C2 = 0.1 F. C1 and C2 are in parallel (VCC = 5 V, in case of 3 V supply,  value of R3 should be reduced, see introductory text.

Single clock operation

TOIM3000 can be operated with only a single clock. In this case, B_CLK and XIN are tight together and connected to the Baudout pin of the UART. The pulse width is then shortened to 3/16 of the bit length and noise filtering is deactivated. S1 should be connected to VCC and SO to GND.

Figure 2 shows a typical example of an RS232 port interface. The TOIM3232 interfaces the RS232 port to an infrared transceiver. Due to the various voltage levels, an additional level converter (discrete or integrated) is necsessary. The baud rate generator is programmable. A description of programming is given in the Chapter "Software for the TOIM3232" page 7 (IrDA Design Guide). When BR/D = 0, the TOIM3232 interprets RD_232 data as data transmitted to the TFDS3000. On the other hand, whenever BR/D = 1, the TOIM3232 interprets RD_232 as the control word. The baud rate can be programmed to operate from 1200 bit/s to 115 kbit/s. As RS232 level converter, EIA232 or MAX232 or equivalent should be used.

The external resistors and capacitors needed are shown in figure 1. Please also refer to figure 1 for the recommended power supply filter and pull-up resistors.

The output pulse length can be programmed, see chapter "Operation Description". It is strongly recommended to use 1.627 s output pulses to save battery power.

The TOIM3xxx series ICs provide proper timing for the front end infrared transceiver TFDS3000, as specified bythe IrDA standard. In the transmit mode, the TOIM3xxx provides IrDA-compatible electrical pulses to the infrared transceiver TFDS3000 on logic LOW electrical input. In the receive mode, the TOIM3xxx stretches received infrared pulses to the proper bit width at the operating bit rate. The IrDA bit rate varies from 2.4 to 115.2 kbit/s.

For the UART interface, the TOIM3xxx uses the 1.8432 MHz clock input as the fast clock and the baud clock output from the UART to do the pulse stretching and shortening. The baud clock is 16 times the baud rate. The output pulses are fixed at 1.627
s or 3/16 of bit time.For the RS232 interface, the TOIM3232 uses an external crystal clock 3.6864 MHz for its pulse stretching and shortening. The TOIM3232 is programmable to operate from 1200 bit/s to 115.2 kbit/s by the communication software through the RS232 port. Output pulses are software-programmable as either 1.627
s or 3/16 of bit time.

The typical power consumption of both TOIM3xxx  circuits is very low with about 10 mW in operational state. It is in the order of magnitude of microwatts in standby mode.