5

3378F–SEEPR–04/04

Note:

The X’s in the address field represent don’t care values and must be clocked.

Functional Description

The AT93C56A/66A is accessed via a simple and versatile 3-wire serial communication

interface. Device operation is controlled by seven instructions issued by the host pro-

cessor. A valid instruction starts with a rising edge of CS and consists of a Start Bit

(logic “1”) followed by the appropriate Op Code and the desired memory address

location.

READ (READ): The Read (READ) instruction contains the address code for the mem-

ory location to be read. After the instruction and address are decoded, data from the

selected memory location is available at the serial output pin DO. Output data changes

are synchronized with the rising edges of serial clock SK. It should be noted that a

dummy bit (logic “0”) precedes the 8- or 16-bit data output string. The AT93C56A/66A

supports sequential read operations. The device will automatically increment the inter-

nal address pointer and clock out the next memory location as long as Chip Select (CS)

is held high. In this case, the dummy bit (logic “0”) will not be clocked out between mem-

ory locations, thus allowing for a continuous stream of data to be read.

ERASE/WRITE (EWEN): To assure data integrity, the part automatically goes into the

Erase/Write Disable (EWDS) state when power is first applied. An Erase/Write Enable

(EWEN) instruction must be executed first before any programming instructions can be

carried out. Please note that once in the EWEN state, programming remains enabled

ERASE (ERASE): The Erase (ERASE) instruction programs all bits in the specified

memory location to the logical “1” state. The self-timed erase cycle starts once the

ERASE instruction and address are decoded. The DO pin outputs the READY/BUSY

A logic “1” at pin DO indicates that the selected memory location has been erased, and

the part is ready for another instruction.

Instruction Set for the AT93C56A and AT93C66A

Instruction

SB

Op

Code

Address

Data

Comments

x 8

x 16

x 8

x 16

READ

1

10

Reads data stored in memory, at

specified address.

EWEN

1

00

11XXXXXXX

11XXXXXX

Write enable must precede all

programming modes.

ERASE

1

11

A

A

Erases memory location A

WRITE

1

01

A

A

D

D

Writes memory location A

ERAL

1

00

10XXXXXXX

10XXXXXX

Erases all memory locations. Valid

WRAL

1

00

01XXXXXXX

01XXXXXX

D

D

Writes all memory locations. Valid

only at V

Register cleared.

EWDS

1

00

00XXXXXXX

00XXXXXX

Disables all programming instructions.