HMS99C52 datasheet(24/43 Pages) HYNIX

24 / 43 page

HMS99C5X Series

Jan. 2003 Ver 1.0

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

Serial data enters and exits through RxD.

TxD outputs the shift clock. 8-bit are transmit-

ted/received (LSB first)

Timer 1/2 overflow rate

8-bit UART

10 bits are transmitted (through TxD) or

received (RxD)

9-bit UART

11 bits are transmitted (TxD) or received (RxD)

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

Baudrate

Oscillator

Timer 1 (16-bit timer)

(8-bit timer with

8-bit auto reload)

1,3

Timer 2

1,3

OSC

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

OSC

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

OSC

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

OSC

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

SMOD

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

OSC

SMOD

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

Timer 1 overflow

()

SMOD

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

OSC

256

TH1

()

[]

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

OSC

65536

RC2H RC2L

()

[]

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

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