CAT35C804A Datasheet, PDF (11/14 Pages) Catalyst Semiconductor – 4K-Bit Secure Access Serial E2PROM

Preliminary
CAT35C804A
then the WRAL instruction. The CAT35C804A will ac-
cept the following commands:
ERAL
ERAL
ERAL An ERAL will be executed
WRAL A WRAL will be executed
Both the ERAL and WRAL commands will program/
erase the entire array and will not be blocked by the
memory pointer.
THE PARITY BIT
The UART compatible protocol supports an even parity
bit if the PE pin of the device is set HIGH, otherwise,
there is no parity. If PE is set LOW and the incoming
instruction contains a parity bit, it may be interpreted as
the stop bit. When PE is HIGH, the CAT35C804A
expects a parity bit at the end of every byte. For example,
the RSEQ instruction will look like this:
0 1100 1011 11
0 A15…A8 P1
0 A7…A0 P1
The device then outputs data continuously until it reaches
the end of the memory. Each byte of data contains 9 bits
with the ninth bit being the parity bit. The RSEQ instruc-
tion may be terminated at any time by bringing CS low;
the output will then go to high impedance.
SYSTEM ERRORS
Whenever an error occurs, be it an instruction error
(unknown instruction), or parity error (perhaps caused
by transmission error), the device will stop its operation.
To return to normal operation, the device must be reset
by pulsing CS LOW and then set back to HIGH. Reset-
ting the device will not affect the ENAC, EWEN and
ENBSY status. The error may be determined by entering
the READ STATUS REGISTER (RSR) instruction
immediatly following the reset. The status output is an
8-bit word with the first three bits being 101. This three
bit pattern indicates that the device is functioning nor-
mally. The fourth bit is “1” if a parity error occurred. The
fifth bit is a “1” if an instruction error occurred. The sixth
bit is a “1” if the device is in a program/erase cycle. The
last two bits are reserved for future use.
The reason for the “101” pattern is to distinguish be-
tween an error conditon (DO tri-stated) and a device
busy status. If an error condition exists, it will not respond
to any input instruction from DI. However, if the device is
in a program/erase cycle, it responds to the RSR instruc-
tion by outputting “101 00100”. If RSR is executed at the
end of a program/erase cycle, the output will be “101000
00”.
10 1 X X X X X
PARITY
ERROR
INSTRUCTION RDY/BUSY
ERROR
STATUS
FUTURE USE
5074 FHD F09
Figure 13. Asynchronous Communication Protocol
CHARACTER n
(1)
START
BIT
BITS 0–7
Note:
(1) Parity bit if enabled; skipped if parity disabled.
STOP
BIT
CHARACTER n+1
35C804 F14
11
Doc. No. 25043-00 2/98