HT93LC66

Rev. 1.70

4

July 10, 2009

Functional Description

The HT93LC66 is accessed via a three-wire serial com-

munication interface. The device is arranged into 256

words by 16 bits or 512 words by 8 bits depending whether

the ORG pin is connected to VCC or VSS. The HT93LC66

contains seven instructions: READ, ERASE, WRITE,

EWEN, EWDS, ERAL and WRAL. When the user

selectable internal organization is arranged into

256

´16 (512´8), these instructions are all made up of

11(12) bits data: 1 start bit, 2 op code bits and 8(9) address

bits.

By using the control signal CS, SK and data input signal

DI, these instructions can be given to the HT93LC66.

These serial instruction data presented at the DI input

will be written into the device at the rising edge of SK.

During the READ cycle, DO pin acts as the data output

and during the WRITE or ERASE cycle, DO pin indi-

cates the BUSY/READY status. When the DO pin is ac-

tive for read data or as a BUSY/READY indicator the CS

pin must be high; otherwise DO pin will be in a high-im-

pedance state. For successful instructions, CS must be

low once after the instruction is sent. After power on, the

device is by default in the EWDS state. And, an EWEN

instruction must be performed before any ERASE or

WRITE instruction can be executed. The following are

the functional descriptions and timing diagrams of all

seven instructions.

READ

The READ instruction will stream out data at a specified

address on the DO pin. The data on DO pin changes

during the low-to-high edge of SK signal. The 8 bits or

16 bits data stream is preceded by a logical

²0² dummy

bit. Irrespective of the condition of the EWEN or EWDS

instruction, the READ command is always valid and in-

dependent of these two instructions. After the data word

has been read the internal address will be automatically

incremented by 1 allowing the next consecutive data

word to be read out without entering further address

data. The address will wrap around with CS High until

CS returns to LOW.

EWEN/EWDS

The EWEN/EWDS instruction will enable or disable the

programming capabilities. At both the power on and

power off state the device automatically entered the dis-

able mode. Before a WRITE, ERASE, WRAL or ERAL in-

struction is given, the programming enable instruction

EWEN must be issued, otherwise the ERASE/WRITE in-

struction is invalid. After the EWEN instruction is issued,

the programming enable condition remains until power is

turned off or a EWDS instruction is given. No data can be

written into the device in the programming disabled state.

By so doing, the internal memory data can be protected.

ERASE

The ERASE instruction erases data at the specified ad-

dresses in the programming enable mode. After the

ERASE op-code and the specified address have been

issued, the data erase is activated by the falling edge of

CS. Since the internal auto-timing generator provides all

timing signals for the internal erase, so the SK clock is

not required. During the internal erase, we can verify the

busy/ready status if CS is high. The DO pin will remain

low but when the operation is over, the DO pin will return

to high and further instructions can be executed.

WRITE

The WRITE instruction writes data into the device at the

specified addresses in the programming enable mode.

After the WRITE op-code and the specified address and

data have been issued, the data writing is activated by

the falling edge of CS. Since the internal auto-timing

generator provides all timing signal for the internal writ-

ing, so the SK clock is not required. The auto-timing

write cycle includes an automatic erase-before-write ca-

pability. So, it is not necessary to erase data before the

WRITE instruction. During the internal writing, we can

verify the busy/ready status if CS is high. The DO pin will

remain low but when the operation is over, the DO pin

will return to high and further instructions can be exe-

cuted.

ERAL

The ERAL instruction erases the entire 256

´16 or 512´8

memory cells to logical

²1² state in the programming en-

able mode. After the erase-all instruction set has been

issued, the data erase feature is activated by the falling

edge of CS. Since the internal auto-timing generator

provides all timing signal for the erase-all operation, so

the SK clock is not required. During the internal erase-all

operation, we can verify the busy/ready status if CS is

high. The DO pin will remain low but when the operation

is over, the DO pin will return to high and further instruc-

tion can be executed.

WRAL

The WRAL instruction writes data into the entire 256

´16

or 512

´8 memory cells in the programming enable

mode. After the write-all instruction set has been issued,

the data writing is activated by the falling edge of CS.

Since the internal auto-timing generator provides all tim-

ing signals for the write-all operation, so the SK clock is

not required. During the internal write-all operation, we

can verify the busy/ready status if CS is high. The DO

pin will remain low but when the operation is over the

DO pin will return to high and further instruction can be

executed.