93AA66A/B/C, 93LC66A/B/C, 93C66A/B/C
2.6
Erase/Write Disable and
Enable(EWDS/EWEN)
To protect against accidental data disturbance, the
EWDS
instruction can be used to disable all erase/write
functions and should follow all programming opera-
tions. Execution of a
READ
instruction is independent of
both the
EWEN
and
EWDS
instructions.
The 93XX66A/B/C powers up in the Erase/Write
Disable (EWDS) state. All Programming modes must be
preceded 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.
FIGURE 2-5:
CS
EWDS TIMING
T
CSL
CLK
DI
1
0
0
0
0
x
•••
x
FIGURE 2-6:
EWEN TIMING
T
CSL
CS
CLK
DI
1
0
0
1
1
x
•••
x
2.7
Read
The
READ
instruction outputs the serial data of the
addressed memory location on the DO pin. A dummy
zero bit precedes the 8-bit (If ORG pin is low or A-Version
devices) or 16-bit (If ORG pin is high or B-version
devices) 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
). Sequential read is possible
when CS is held high. The memory data will automati-
cally cycle to the next register and output sequentially.
FIGURE 2-7:
CS
READ TIMING
CLK
DI
1
1
0
An
•••
A0
DO
High-Z
0
Dx
•••
D0
Dx
•••
D0
Dx
•••
D0
©
2005 Microchip Technology Inc.
DS21795C-page 9
MICROCHIP [ MICROCHIP TECHNOLOGY ]
