93C46B

DS21172D-page 6

Preliminary

© 1997 Microchip Technology Inc.

3.6

ERASE/WRITE Disable and Enable

(EWDS/EWEN)

The device powers up in the ERASE/WRITE Disable

(EWDS) state. All programming modes must be pre-

ceded by an Erase/Write Enable (EWEN) instruction.

Once the EWEN instruction is executed, programming

remains enabled until an EWDS instruction is executed

or Vcc is removed from the device. To protect against

accidental data disturbance, the EWDS instruction can

be used to disable all ERASE/WRITE functions and

should follow all programming operations. Execution of

a READ instruction is independent of both the EWDS

and EWEN instructions.

3.7

READ

The READ instruction outputs the serial data of the

addressed memory location on the DO pin. A dummy

zero bit precedes the 16-bit output string. The output

data bits will toggle on the rising edge of the CLK and

tial read is possible when CS is held high. The memory

data will automatically cycle to the next register and

output sequentially.

FIGURE 3-4:

EWDS TIMING

FIGURE 3-5:

EWEN TIMING

FIGURE 3-6:

READ TIMING

CS

CLK

DI

1

0

0

0

0

X

•••

X

1

X

CS

CLK

DI

0

0

1

1

X

•••

CS

CLK

DI

DO

1

1

0

An

•••

A0

HIGH-Z

0

Dx

•••

D0

Dx

•••

D0

•••

Dx

D0