KS57C2308/P2308/C2316/P2316 SERIAL I/O INTERFACE
13-3
SERIAL I/O MODE REGISTER (SMOD)
The serial I/O mode register, SMOD, is an 8-bit register that specifies the operation mode of the serial interface.
Its reset value is logical zero. SMOD is organized in two 4-bit registers, as follows:
FE0H SMOD.3 SMOD.2 SMOD.1 SMOD.0
FE1H SMOD.7 SMOD.6 SMOD.5 0
SMOD register settings enable you to select either MSB-first or LSB-first serial transmission, and to operate in
transmit-and-receive mode or receive-only mode. SMOD is a write-only register and can be addressed only by
8-bit RAM control instructions. One exception to this is SMOD.3, which can be written by a 1-bit RAM control
instruction. When SMOD.3 is set to 1, the contents of the serial interface interrupt request flag, IRQS, and the
3-bit serial clock counter are cleared, and SIO operations are initiated. When the SIO transmission starts,
SMOD.3 is cleared to logical zero.
Table 13-1. SIO Mode Register (SMOD) Organization
SMOD.0 0Most significant bit (MSB) is transmitted first
1Least significant bit (LSB) is transmitted first
SMOD.1 0Receive-only mode; output buffer is off
1Transmit-and-receive mode; output buffer is on
SMOD.2 0Disable the data shifter and clock counter; retain contents of IRQS flag when serial
transmission is halted
1Enable the data shifter and clock counter; set IRQS flag to "1" when serial
transmission is completed
SMOD.3 1Clear IRQS flag and 3-bit clock counter to "0"; initiate transmission and then reset
this bit to logic zero
SMOD.4 0Bit not used; value is always "0"
SMOD.7 SMOD.6 SMOD.5 Clock Selection R/W Status of SBUF
000External clock at SCK pin SBUF is enabled when SIO
operation is halted or when SCK
goes high.
001Use TOL0 clock from TC0
01–CPU clock: fxx/4, fxx/8, fxx/64 Enable SBUF read/write
1004.09 kHz clock: fxx/210 SBUF is enabled when SIO
operation is halted or when SCK
goes high.
111262 kHz clock: fxx/24
NOTES:
1. “fxx” = system clock.
2. kHz frequency ratings assume a system clock (fxx) running at 4.19 MHz.
3. The SIO clock selector circuit cannot select a fxx/24 clock if the CPU clock is fxx/64.