ically incremented to the next higher address after

each byte of data is shifted out. When the highest

address is reached (1FFh), the address counter

rolls over to 0h allowing the read cycle to be con-

tinued indefinitely. The read operation is terminated

by deselecting the chip. The chip can be deselected

at any time during data output. Any read attempt

during a non-volatile write cycle will be rejected and

will deselect the chip.

Byte Write Operation

Prior to any write attempt, the write enable latch

must have been set by issuing the WREN instruc-

tion. First, the device is selected (S = low) and a

serial WREN instruction byte is issued. Then, the

product is deselected by taking S high. After the

WREN instruction byte is sent, the ST95P08 will

set the write enable latch and then remain in

standby until it is deselected. Then, the write state

is entered by selecting the chip, issuing a one byte

address (A7-A0), and one byte of data. Bits 3 and

4 of the write instruction contain address bits A9

and A8 (most significant address bits). S must

remain low for the entire duration of the operation.

The product must be deselected just after the eigth

bit of data has been latched in. If not, the write

process is cancelled. As soon as the product is

deselected, the self-timed write cycle is initiated.

While the write is in progress, the status register

may be read to check BP1, BP0, WEL and WIP.

WIP is high during the self-timed write cycle. When

the cycle is close to completion, the write enable

latch is reset.

Page Write Operation

A maximum of 16 bytes of data may be written

during one non-volatile write cycle. All 16 bytes

must reside on the same page. The page write

mode is the same as the byte write mode except

that instead of deselecting after the first byte of

data, up to 15 additional bytes can be shifted in

prior to deselecting the chip. A page address begins

with address xxxx 0000 and ends with xxxx 1111.

If the address counter reaches xxxx 1111 and the

clock continues, the counter will roll over to the first

address of the page (xxxx 0000) and overwrite any

previous written data. The programming cycle will

only start if the S transition does occur at the clock

low pulse just after the eigth bit of data of a word is

received.

C

D

AI01318

S

Q

A7

2

1

3456789 10 11 12 13 14 15 16 17 18 19

A6 A5 A4 A3 A2 A1 A0

A9 A8

20 21 22 23

7

65432

0

1

HIGH IMPEDANCE

DATA OUT

INSTRUCTION

BYTE ADDRESS

0

Figure 8. Read Operation Sequence

9/16

ST95P08