FEDS5412222B-02
LAPIS Semiconductor
MSM5412222B
5/16
OPERATION
Write Operation
The write operation is controlled by three clocks, SWCK, RSTW, and WE. Write operation is accomplished by
cycling SWCK, and holding WE high after the write address pointer reset operation or RSTW.
Each write operation, which begins after RSTW, must contain at least 150 active write cycles, i.e. SWCK cycles
while WE is high. To transfer the last data to the DRAM array, which at that time is stored in the serial data
registers attached to the DRAM array, an RSTW operation is required after the last SWCK cycle.
Note that every write timing of MSM5412222B is delayed by one clock compared with read timings for easy
cascading without any interface delay devices.
Write Reset: RSTW
The first positive transition of SWCK after RSTW becomes high resets the write address counters to zero. RSTW
setup and hold times are referenced to the rising edge of SWCK. Because the write reset function is solely
controlled by the SWCK rising edge after the high level of RSTW, the states of WE and IE are ignored in the write
reset cycle.
Before RSTW may be brought high again for a further reset operation, it must be low for at least two SWCK
cycles.
Data Inputs: D
IN
0 to 11
Write Clock: SWCK
The SWCK latches the input data on chip when WE is high, and also increments the internal write address pointer.
Data-in setup time t
DS
, and hold time t
DH
are referenced to the rising edge of SWCK.
Write Enable: WE
WE is used for data write enable/disable control. WE high level enables the input, and WE low level disables the
input and holds the internal write address pointer. There are no WE disable time (low) and WE enable time (high)
restrictions, because the MSM5412222B is in fully static operation as long as the power is on. Note that WE setup
and hold times are referenced to the rising edge of SWCK.
Input Enable: IE
IE is used to enable/disable writing into memory. IE high level enables writing. The internal write address pointer
is always incremented by cycling SWCK regardless of the IE level. Note that IE setup and hold times are
referenced to the rising edge of SWCK.
