MSM518221A Datasheet, PDF (6/17 Pages) OKI electronic componets – 262,214-Word x 8-Bit Field Memory

¡ Semiconductor
MSM518221A
Read Operation
The read operation is controlled by three clocks, SRCK, RSTR, and RE. Read operation is
accomplished by cycling SRCK, and holding RE high after the read address pointer reset operation
or RSTR.
Each read operation, which begins after RSTR, must contain at least 80 active read cycles, i.e. SRCK
cycles while RE is high.
Read Reset : RSTR
The first positive transition of SRCK after RSTR becomes high resets the read address counters to
zero. RSTR setup and hold times are referenced to the rising edge of SRCK. Because the read reset
function is solely controlled by the SRCK rising edge after the high level of RSTR, the states of RE and
OE are ignored in the read reset cycle.
Before RSTR may be brought high again for a further reset operation, it must be low for at least two
SRCK cycles.
Data Out : D_OUT0 - 7
Read Clock : SRCK
Data is shifted out of the data registers. It is triggered by the rising edge of SRCK when RE is high
during a read operation. The SRCK input increments the internal read address pointer when RE is
high.
The three-state output buffer provides direct TTL compatibility (no pullup resistor required). Data
out is the same polarity as data in. The output becomes valid after the access time interval t_AC that
begins with the rising edge of SRCK. There are no output valid time restrictions on MSM518221A.
Read Enable : RE
The function of RE is to gate of the SRCK clock for incrementing the read pointer. When RE is high
before the rising edge of SRCK, the read pointer is incremented. When RE is low, the read pointer
is not incremented. RE setup times (t_RENS and t_RDSS) and RE hold times (t_RENH and t_RDSH) are
referenced to the rising edge of the SRCK clock.
Output Enable : OE
OE is used to enable/disable the outputs. OE high level enables the outputs. The internal read
address pointer is always incremented by cycling SRCK regardless of the OE level. Note that OE
setup and hold times are referenced to the rising edge of SRCK.
6/16