GMS90 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
SCON
Mode
Baudrate
Description
SM0
SM1
Serial data enters and exits through RxD.
TxD outputs the shift clock. 8-bit are transmit-
ted/received (LSB first)
f
--O----S----C--
0
1
0
0
12
8-bit UART
10 bits are transmitted (through TxD) or
received (RxD)
0
1
Timer 1/2 overflow rate
9-bit UART
f
fOSC
--O----S----C--
------------
2
3
1
1
0
1
or
11 bits are transmitted (TxD) or received (RxD)
32
64
9-bit UART
Like mode 2 except the variable baud rate
Timer 1/2 overflow rate
Table 7. Formulas for Calculating Baud rates
Baud Rate
Interface Mode
derived from
Baudrate
fOSC
0
------------
12
Oscillator
2SMOD
64
2
------------------
× fOSC
2SMOD
------------------
32
1,3
× (Timer 1 overflow)
Timer 1 (16-bit timer)
(8-bit timer with
8-bit auto reload)
2SMOD
f
------------------ ---------------------O----S----C---------------------
1,3
×
32
12 × [256 – (TH1)]
fOSC
Timer 2
1,3
---------------------------------------------------------------------------------
32 × [65536 – (RC2H, RC2L)]
Dec. 1998 Ver 3.0
21
HYNIX [ HYNIX SEMICONDUCTOR ]
