M69KB128AA datasheet(19/68 Pages) STMICROELECTRONICS

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M69KB128AA

6 Synchronous operating modes

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6.2

Full Synchronous mode

In Full Synchronous mode, the device performs read and write operations synchronously.

Synchronous Read and Write operations are performed at Word level.

The initial Burst Read and Write access latches the Burst start address. The number of Words

to be output or input during Synchronous Read and Write operations is controlled by bits 0 to 2

of the BCR.

During Burst Read and Write operations, the first data will be output after a number of clock

cycles defined by the Latency value.

Programming the registers (BCR and RCR) and reading the registers (BCR, RCR and DIDR)

can be performed using the CR controlled method in Full Synchronous mode.

Full Synchronous operations are described in Table 7: Full Synchronous mode.

6.3

Synchronous Burst Read and Write

During Synchronous Burst Read or Write operations, addresses are latched on the rising edge

of the Clock K when L is Low and data are latched on the rising edge of K. The Write Enable,

W, signal indicates whether the operation is going to be a read (W=VIH) or a write (W=VIL).

The WAIT output will be asserted as soon as a Synchronous Burst operation is initiated and will

be deasserted to indicate when data are to be transferred to (or from) the memory array.

The Burst Length is the number of Words to be output or input during a Synchronous Burst

Read or Write operation. It can be configured as 4, 8, 16 or 32 Words or continuous through bit

BCR0 to BCR2 or the Burst Configuration Register. The Latency defines the number of clock

cycles between the beginning of a Burst Read operation and the first data output (counting from

the first Clock edge where L was detected Low) or between the beginning of a Burst Write

operation and the first data input. The Latency can be set through bits BCR13 to BCR11 of the

Bus Configuration Register (see Table 4: Operating Frequency versus Latency).

The latency can also be configured to fixed or variable by programming bit BCR14. By default,

the Latency Type is set to variable.

Synchronous Read operations are performed in both fixed and variable latency mode while

Synchronous Write operations are only performed with fixed latency.

See Figure 24, Note 1, and Figure 30, Note 31, for details on Synchronous Read and Write AC

waveforms, respectively.

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