GMS90C320

OCT. 2000 Ver 1.2

17

Serial Interface (USART)

The serial port is full duplex and can operate in four modes (one synchronous mode, three asynchronous modes) as illustrated

in Table 6. The possible baud rates can be calculated using the formulas given in Table 7.

Table 6

USART Operating Modes

Mode

SCON

Baudrate

Description

SM0

SM1

0

0

0

Serial data enters and exits through RxD.

TxD outputs the shift clock.

8-bit are transmitted/received (LSB first)

1

0

1

Timer 1/2 overflow rate

8-bit UART

10 bits are transmitted (through TxD) or

received (RxD)

2

10

or

9-bit UART

11 bits are transmitted (through TxD) or

received (RxD)

3

1

1

Timer 1/2 overflow rate

9-bit UART

Like mode 2 except the variable baud rate

Table 7

Formulas for Calculating Baud rates

Baud Rate

derived from

Interface Mode

Baud rate

Oscillator

0

2

Timer 1 (16-bit timer)

(8-bit timer with 8-bit autore-

load)

1, 3

1, 3

Timer 2

1, 3

ƒ

OSC

12

----------------

ƒ

OSC

32

----------------

ƒ

OSC

64

----------------

ƒ

OSC

12

----------------

ƒ

OSC

×

64

------------------------------------------

timer 1 overflow rate

×

32

---------------------------------------------------------------------------------

ƒ

OSC

×

32

12

256

TH1

–

()

×

×

-----------------------------------------------------------

ƒ

OSC

32

65536

RC2H,RC2L

()

–

[]

×

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