CAT93C46B Datasheet, PDF (4/14 Pages) ON Semiconductor – Microwire Serial EEPROM

CAT93C46B
Device Operation
The CAT93C46B is a 1024−bit nonvolatile memory
intended for use with industry standard microprocessors.
The CAT93C46B can be organized as either registers of 16
bits or 8 bits. When organized as X16, seven 9−bit
instructions control the reading, writing and erase
operations of the device. When organized as X8, seven
10−bit instructions control the reading, writing and erase
operations of the device. The CAT93C46B operates on a
single power supply and will generate on chip the high
voltage required during any write operation.
Instructions, addresses, and write data are clocked into the
DI pin on the rising edge of the clock (SK). The DO pin is
normally in a high impedance state except when reading data
from the device, or when checking the ready/busy status
during a write operation. The serial communication protocol
follows the timing shown in Figure 2.
The ready/busy status can be determined after the start of
internal write cycle by selecting the device (CS high) and
polling the DO pin; DO low indicates that the write
operation is not completed, while DO high indicates that the
device is ready for the next instruction. If necessary, the DO
pin may be placed back into a high impedance state during
chip select by shifting a dummy “1” into the DI pin. The DO
pin will enter the high impedance state on the rising edge of
the clock (SK). Placing the DO pin into the high impedance
state is recommended in applications where the DI pin and
the DO pin are to be tied together to form a common DI/O
pin. The Ready/Busy flag can be disabled only in Ready
state; no change is allowed in Busy state.
The format for all instructions sent to the device is a
logical “1” start bit, a 2−bit (or 4−bit) opcode, 6−bit address
(an additional bit when organized X8) and for write
operations a 16−bit data field (8−bit for X8 organization).
Read
Upon receiving a READ command (Figure 3) and an
address (clocked into the DI pin), the DO pin of the
CAT93C46B will come out of the high impedance state and,
after sending an initial dummy zero bit, will begin shifting
out the data addressed (MSB first). The output data bits will
toggle on the rising edge of the SK clock and are stable after
the specified time delay (t_PD0 or t_PD1).
After the initial data word has been shifted out and CS
remains asserted with the SK clock continuing to toggle, the
device will automatically increment to the next address and
shift out the next data word in a sequential READ mode. As
long as CS is continuously asserted and SK continues to
toggle, the device will keep incrementing to the next address
automatically until it reaches to the end of the address space,
then loops back to address 0. In the sequential READ mode,
only the initial data word is proceeded by a dummy zero bit.
All sunsequent data words will follow without a dummy
zero bit.
Erase/Write Enable and Disable
The CAT93C46B powers up in the write disable state.
Any writing after power−up or after an EWDS (write
disable) instruction must first be preceded by the EWEN
(write enable) instruction. Once the write instruction is
enabled, it will remain enabled until power to the device is
removed, or the EWDS instruction is sent. The EWDS
instruction can be used to disable all CAT93C46B write and
erase instructions, and will prevent any accidental writing or
clearing of the device. Data can be read normally from the
device regardless of the write enable/disable status. The
EWEN and EWDS instructions timing is shown in Figure 4.
Table 8. INSTRUCTION SET
Instruction Start Bit
READ
1
ERASE
1
WRITE
1
EWEN
1
EWDS
1
ERAL*
1
WRAL*
1
* Not available at V_CC < 1.8 V
Opcode
10
11
01
00
00
00
00
Address
x8
x16
A6−A0
A5−A0
A6−A0
A5−A0
A6−A0
A5−A0
11XXXXX
11XXXX
00XXXXX
00XXXX
10XXXXX
10XXXX
01XXXXX
01XXXX
Data
x8
x16
D7−D0 D15−D0
D7−D0 D15−D0
Comments
Read Address AN–A0
Clear Address AN–A0
Write Address AN–A0
Write Enable
Write Disable
Clear All Addresses
Write All Addresses
http://onsemi.com
4