Preliminary

CAT35C804A

12

Doc. No. 25043-00 2/98

INSTRUCTION SET

DISAC Disable Access

1000 1000

This instruction will lock the memory from all program/

erase operations regardless of the contents of the memory

pointer. A write can be accomplished only by first enter-

ing the ENAC instruction followed by a valid access

code.

ENAC Enable Access

1100 0101

[Access Code]

In the protected mode, this instruction, followed by a

valid access code, unlocks the device for read/write/

clear access.

WMPR Write Memory Pointer Register

1100 0100

[A15–A8] [A7–A0]

(x8 organization)

[A7–A0]

(x16 organization)

1100 0100

The WMPR instruction followed by 8 or 16 bits of

address (depending on the organization) will move the

pointer to the newly specified address.

MACC Modify Access Code

1101

[Length] [Old code] [New code]

[New code]

This instruction requires the user to enter the old access

code, if one was set previously, followed by the new

access code and a re-entry of the new access code for

verification. Within the instruction format, the variable

[Length] designates the length of the access code as the

following:

[Length] = [0] No access code. Set device to unpro-

tected mode.

[Length] = [1–8] Length of access code is 1 to 8 bytes.

[Length] = [>8] Illegal number of bytes. The CAT35C804A

will ignore the rest of the transmission.

RMPR Read Memory Pointer Register

1100 1010

Output the content of the memory pointer register to the

serial output port.

Figure 14. ERAL Timing (x8 Format)

35C804 F15

Figure 15. ERAL Timing (x16 Format)

35C804 F16

CS

DI

HIGH-Z

DO

OP0–OP7

tEW

BUSY(1)

OP CODE

OP0–OP7

OP CODE

NEXT INSTRUCTION

CS

DI

HIGH-Z

DO

OP0–OP7

tEW

BUSY(1)

OP CODE

OP0–OP7

OP CODE

NEXT INSTRUCTION

Note:

(1) DO becomes low to indicate busy status if ENBSY was previously executed. If ENBSY was not previously executed, DO will be in the

High-Z condition.