5
AT93C46C
1122D–SEEPR–08/02
Functional
Description
The AT93C46C 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 16-bit data output string.
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 Erase/Write Enable state, programming
remains enabled until an Erase/Write Disable (EWDS) instruction is executed or V
CC
power is removed from the part.
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
status of the part if CS is brought high after being kept low for a minimum of 250 ns (t
CS
).
A 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 16 bits of data to be writ-
ten into the specified memory location. The self-timed programming cycle t
WP
starts
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 250 ns (t
CS
). A logic “0” at DO indicates that programming is still in progress. A logic
“1” indicates that the memory location at the specified address has been written with the
data pattern contained in the instruction and the part is ready for further instructions. A
Ready/Busy Status cannot be obtained if the CS is brought high after the end of
the self-timed programming cycle, t
WP
.
Instruction Set for the AT93C46C
Instruction SB Op Code
Address
Commentsx16
READ 1 10 A
5
-A
0
Reads data stored in memory, at specified address.
EWEN 1 00 11XXXX Write enable must precede all programming modes.
ERASE 1 11 A
5
-A
0
Erase memory location A
n
-A
0
.
WRITE 1 01 A
5
-A
0
Writes memory location A
n
-A
0
.
ERAL 1 00 10XXXX Erases all memory locations. Valid only at V
CC
= 4.5V to 5.5V.
WRAL 1 00 01XXXX Writes all memory locations. Valid only at V
CC
= 4.5V to 5.5V.
EWDS 1 00 00XXXX Disables all programming instructions.
