Samsung KS57C2308 manual Serial I/O Mode Register Smod, SMOD.0, SMOD.1, SMOD.2, SMOD.3, SMOD.4

KS57C2308/P2308/C2316/P2316 SERIAL I/O INTERFACE

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	0	Most significant bit (MSB) is transmitted first
	1	Least significant bit (LSB) is transmitted first
SMOD.1	0	Receive-only mode; output buffer is off
	1	Transmit-and-receive mode; output buffer is on
SMOD.2	0	Disable the data shifter and clock counter; retain contents of IRQS flag when serial
		transmission is halted
	1	Enable the data shifter and clock counter; set IRQS flag to "1" when serial
		transmission is completed
SMOD.3	1	Clear IRQS flag and 3-bit clock counter to "0"; initiate transmission and then reset
		this bit to logic zero
SMOD.4	0	Bit not used; value is always "0"

SMOD.7	SMOD.6	SMOD.5	Clock Selection	R/W Status of SBUF
0	0	0	External clock at SCK pin	SBUF is enabled when SIO
				operation is halted or when SCK
				goes high.
0	0	1	Use TOL0 clock from TC0
0	1	–	CPU clock: fxx/4, fxx/8, fxx/64	Enable SBUF read/write
1	0	0	4.09 kHz clock: fxx/210	SBUF is enabled when SIO
				operation is halted or when SCK
				goes high.
1	1	1	262 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.

13-3