HMS99C52 Datasheet, PDF (24/43 Pages) Hynix Semiconductor – 8-BIT SINGLE-CHIP MICROCONTROLLERS

HMS99C5X Series
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
0
1
2
3
SCON
SM0 SM1
0
0
0
1
1
0
1
1
Baudrate
Description
f_{--O----S----C--}
12
Timer 1/2 overflow rate
f_{--O----S----C--}
32
or
f_{--O----S----C--}
64
Timer 1/2 overflow rate
Serial data enters and exits through RxD.
TxD outputs the shift clock. 8-bit are transmit-
ted/received (LSB first)
8-bit UART
10 bits are transmitted (through TxD) or
received (RxD)
9-bit UART
11 bits are transmitted (TxD) or received (RxD)
9-bit UART
Like mode 2 except the variable baud rate
Table 7. Formulas for Calculating Baud rates
Baud Rate
derived from
Interface Mode
0
Oscillator
2
1,3
Timer 1 (16-bit timer)
(8-bit timer with
8-bit auto reload)
1,3
Timer 2
1,3
Baudrate
f_{--O-----S---C--}
12
2_----^S_----^M_----^O_----^D_--
64
×
f_OSC
2_----^S_----^M_----^O_----^D_--
32
×
(
Timer
1
overflow
)
2_----^S_---^M_-----^O_----^D_--
32
×
--------------------^f--^O----^S----^C---------------------
12 × [256 Ð (TH1)]
------------------------------------^f--^O----^S---^C-------------------------------------
32 × [65536 Ð (RC2H, RC2L)]
20
Jan. 2003 Ver 1.0