6/16

¡ Semiconductor

MSM518222

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.

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

begins with the rising edge of SRCK. *There are no output valid time restrictions on MSM518222.

Read Enable : RE

The function of RE is to gate 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

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.