Datasheet

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73S1215F Data Sheet DS_1215F_003

42 Rev. 1.4

Miscellaneous Control Register 0 (MISCtl0): 0xFFF1 Å 0x00

Transmit and receive (TX and RX) pin selection and loop back test configuration are set up via this register.

Table 38: The MISCtl0 Register

MSB LSB

PWRDN – – – – – SLPBK SSEL

Bit Symbol Function

MISCtl0.7 PWRDN This bit places the 73S1215F into a power down state.

MISCtl0.6 –

MISCtl0.5 –

MISCtl0.4 –

MISCtl0.3 –

MISCtl0.2 –

MISCtl0.1 SLPBK

1 = UART loop back testing mode. The pins TXD and RXD are to be

connected together externally (with SLPBK =1) and therefore:

SLPBK SSEL Mode

0 0 normal using Serial_0

0 1 normal using Serial_1

1 0 Serial_0 TX feeds Serial_1 RX

1 1 Serial_1 TX feeds Serial_0 RX

MISCtl0.0 SSEL

Selects either Serial_1 if set =1 or Serial_0 if set = 0 to be connected

to RXD and TXD pins.

1.7.4.1 Serial Interface 0

The Serial Interface 0 can operate in four modes:

• Mode 0

Pin RX serves as input and output. TX outputs the shift clock. 8 bits are transmitted with LSB first. The

baud rate is fixed at 1/12 of the crystal frequency. Reception is initialized in Mode 0 by setting the flags in

S0CON as follows: RI0 = 0 and REN0 = 1. In other modes, a start bit when REN0 = 1 starts receiving

serial data.

• Mode 1

Pin RX serves as input, and TX serves as serial output. No external shift clock is used, 10 bits are

transmitted: a start bit (always 0), 8 data bits (LSB first), and a stop bit (always 1). On receive, a start bit

synchronizes the transmission, 8 data bits are available by reading S0BUF, and stop bit sets the flag

RB80 in the Special Function Register S0CON. In mode 1 either internal baud rate generator or timer 1

can be use to specify baud rate.

• Mode 2

This mode is similar to Mode 1, with two differences. The baud rate is fixed at 1/32 or 1/64 of oscillator

frequency and 11 bits are transmitted or received: a start bit (0), 8 data bits (LSB first), a programmable

9th bit, and a stop bit (1). The 9th bit can be used to control the parity of the serial interface: at

transmission, bit TB80 in S0CON is output as the 9th bit, and at receive, the 9th bit affects RB80 in

Special Function Register S0CON.

• Mode 3

The only difference between Mode 2 and Mode 3 is that in Mode 3 either internal baud rate generator

or timer 1 can be use to specify baud rate.

The S0BUF register is used to read/write data to/from the serial 0 interface.