5

AT93C86A

3408H–SEEPR–1/07

Functional

Description

The AT93C86A is accessed via a simple and versatile three-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 AT93C86A sup-

ports sequential read operations. The device will automatically increment the internal

address pointer and clock out the next memory location as long as CS is held high. In

this case, the dummy bit (logic “0”) will not be clocked out between memory 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 sta-

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

part is ready for another instruction.

WRITE (WRITE): The Write (WRITE) instruction contains the 8 or 16 bits of data to be

after the last bit of data is received at serial data input pin DI. The DO pin outputs the

Ready/Busy status of the part if CS is brought high after being kept low for a minimum of

Table 5. Instruction Set for the AT93C86A

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

11XXXXXXXXX

11XXXXXXXX

Write enable must precede all

programming modes.

ERASE

1

11

WRITE

1

01

ERAL

1

00

10XXXXXXXXX

10XXXXXXXX

Erases all memory locations.

WRAL

1

00

01XXXXXXXXX

01XXXXXXXX

Writes all memory locations.

Disable Register cleared.

EWDS

1

00

00XXXXXXXXX

00XXXXXXXX

Disables all programming

instructions.