Rainbow Electronics HT93LC46 - Manual (Page 5)

Timing Diagrams
Functional Description
The HT93LC46 is accessed via a three-wire serial
communication interface. The device is arranged
into 64 words by 16 bits or 128 words by 8 bits
depending whether the ORG pin is connected to
VCC or VSS. The HT93LC46 contains seven in-
structions: READ, ERASE, WRITE, EWEN,
EWDS, ERAL and WRAL. When the user se-
lectable internal organization is arranged
into 64
Ч
16 (128
Ч
8), these instructions are all
made up of 9(10) bits data: 1 start bit, 2 op code
bits and 6(7) address bits.
By using the control signal CS, SK and data
input signal DI, these instructions can be given
to the HT93LC46. 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
indicates the BUSY/READY status. When the
DO pin is active fo r read data or as a
BUSY/READY indicator the CS pin must be
high; otherwise DO pin will be in a high-imped-
ance 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 per-
formed before any ERASE or WRITE instruc-
tion 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 “0” dummy bit. Irrespec-
tive of the condition of the EWEN or EWDS
instruction, the READ command is always
valid and independent of these two instruc-
tions. After the data word has been read the
internal address will be automatically incre-
mented 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 auto-
matically entered the disable mode. Before a
WRITE, ERASE, WRAL or ERAL instruction is
given, the programming enable instruction
EWEN must be issued, otherwise the
ERASE/WRITE instruction 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 dis-
abled state. By so doing, the internal memory
data can be protected.
HT93LC46
5 6th May ’99