93AA66A/B/C, 93LC66A/B/C, 93C66A/B/C
DS21795B-page 8 2003 Microchip Technology Inc.
2.6 ERASE/WRITE DISABLE And ENABLE (EWDS/EWEN)
The 93XX66A/B/C powers up in the ERASE/WRITE
Disable (EWDS) state. All Programming modes must be
precede d by an ERASE/WRITE En able (EWEN) instruc-
tion. Once the EWEN instruction is executed, program-
ming 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
operatio ns. Executio n of a READ instruct ion i s ind epen-
dent of both the EWEN and EWDS instructions.
FIGURE 2-5: EWDS TIMING
FIGURE 2-6: EWEN T IMIN G
2.7 READ
The READ instruction outputs the serial data of the
addressed memory location on the DO pin. A dummy
zero bit prece des the 8-bit (If ORG pin is low or A-V ersion
devices) or 16-bit (If ORG pin is high or B-version
devic es) ou tput st ring. The ou tput dat a bi ts 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.
FIGU RE 2- 7 : READ TIMIN G
CS
CLK
DI
10
000X
•••
X
T
CSL
1X
CS
CLK
DI
00 1 1X
TCSL
•••
CS
CLK
DI
DO
110
An
•••
A0
HIGH-Z
0Dx
•••
D0 Dx
•••
D0
•••
Dx D0
