Datasheet

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
are stable after the specified time delay (T
PD). Sequen-
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
T
CSL
1 X
CS
CLK
DI
0 0 1 1 X
TCSL
•••
CS
CLK
DI
DO
1 1 0
An
•••
A0
HIGH-Z
0 Dx
•••
D0 Dx
•••
D0
•••
Dx D0