KS57C2308/P2308/C2316/P2316 SERIAL I/O INTERFACE
13-5
SERIAL I/O BUFFER REGISTER (SBUF)
The serial I/O buffer register, SBUF, can be read or written using 8-bit RAM control instructions. Following a
RESET, the value of SBUF is undetermined.
When the serial interface operates in transmit-and-receive mode (SMOD.1 = "1"), transmit data in the SIO buffer
register are output to the SO pin (P0.2) at the rate of one bit for each falling edge of the SIO clock. Receive data
are simultaneously input from the SI pin (P0.3) to SBUF at the rate of one bit for each rising edge of the SIO
clock. When receive-only mode is used, incoming data are input to the SIO buffer at the rate of one bit for each
rising edge of the SIO clock.
++ PROGRAMMING TIP — Setting Transmit/Receive Modes for Serial I/O
1. Transmit the data value 48H through the serial I/O interface using an internal clock frequency of fxx/24
and in MSB-first mode:
BITS EMB
SMB 15
LD EA,#48H ;
LD SBUF,EA ;
LD EA,#0EEH
LD SMOD,EA ;SIO data transfer
KS57C2308/C2316
/ P0.1
SO / P0.2
EXTERNAL
DEVICE
SCK
2. Use CPU clock to transfer and receive serial data at high speed:
BITR EMB
LD EA,TDATA ;TDATA address = BANK0 (20H–7FH)
LD SBUF,EA
LD EA,#4FH
LD SMOD,EA ;SIO start
BITS IES
STEST BTSTZ IRQS
JR STEST
LD EA,SBUF
SMB 0
LD RDATA,EA ;RDATA address = BANK0 (20H–7FH)