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23A1024

1Mbit SPI Serial SRAM with SDI and SQI Interface

Microchip Technology 

2.0 FUNCTIONAL DESCRIPTION

2.1 Principles of Operation

The 23A1024/23LC1024 is an 1 Mbit Serial SRAM

designed to interface directly with the Serial Peripheral

Interface (SPI) port of many of today’s popular

microcontroller families, including Microchip’s PIC®

microcontrollers. It may also interface with

microcontrollers that do not have a built-in SPI port by

using discrete I/O lines programmed properly in

firmware to match the SPI protocol. In addition, the

23A1024/23LC1024 is capable of operation in SDI and

SQI modes. In SDI mode, the SI and SO data lines are

bidirectional, allowing the transfer of two bits per clock

pulse. In SQI mode, two additional data lines enable

the transfer of four bits per clock pulse.

The 23A1024/23LC1024 contains an 8-bit instruction

register. The device is accessed via the SI pin, with

data being clocked in on the rising edge of SCK. The

CS pin must be low for the entire operation.

Table 2-1 contains a list of the possible instruction

bytes and format for device operation. All instructions,

addresses and data are transferred MSB first, LSB last.

2.2 Modes of Operation

The 23X1024 has three modes of operation that are

selected by setting bits 7 and 6 in the MODE register.

The modes of operation are Byte, Page and Burst.

Byte Operation – is selected when bits 7 and 6 in the

MODE register are set to 00. In this mode, the

read/write operations are limited to only one byte. The

Command followed by the 24-bit address is clocked into

the device and the data to/from the device is transferred

on the next eight clocks (Figure 2-1, Figure 2-2).

Page Operation – is selected when bits 7 and 6 in the

MODE register are set to 10. The 23X1024 has

4096 pages of 32 bytes. In this mode, the read and write

operations are limited to within the addressed page (the

address is automatically incremented internally). If the

data being read or written reaches the page boundary,

then the internal address counter will increment to the

start of the page (Figure 2-3, Figure 2-4).

Sequential Operation – is selected when bits 7 and 6

in the MODE register are set to 01. Sequential

operation allows the entire array to be written to and

read from. The internal address counter is automatically

incremented and page boundaries are ignored. When

the internal address counter reaches the end of the

array, the address counter will roll over to 0x00000

(Figure 2-5, Figure 2-6).

23A1024/23LC1024

2.3 Read Sequence

The device is selected by pulling CS low. The 8-bit

READ instruction is transmitted to the

23A1024/23LC1024 followed by the 24-bit address,

with the first seven MSB’s of the address being “don’t

care” bits. After the correct READ instruction and

address are sent, the data stored in the memory at the

selected address is shifted out on the SO pin.

If operating in Sequential mode, the data stored in the

memory at the next address can be read sequentially

by continuing to provide clock pulses. The internal

Address Pointer is automatically incremented to the

next higher address after each byte of data is shifted

out. When the highest address is reached (1FFFFh),

the address counter rolls over to address 00000h,

allowing the read cycle to be continued indefinitely.

The read operation is terminated by raising the CS

pin.

2.4 Write Sequence

Prior to any attempt to write data to the

23A1024/23LC1024, the device must be selected by

bringing CS low.

Once the device is selected, the Write command can

be started by issuing a WRITE instruction, followed by

the 24-bit address, with the first seven MSB’s of the

address being “don’t care” bits, and then the data to be

written. A write is terminated by the CS being brought

high.

If operating in Page mode, after the initial data byte is

shifted in, additional bytes can be shifted into the

device. The Address Pointer is automatically

incremented. This operation can continue for the entire

page (32 bytes) before data will start to be overwritten.

If operating in Sequential mode, after the initial data

byte is shifted in, additional bytes can be clocked into

the device. The internal Address Pointer is

automatically incremented. When the Address Pointer

reaches the highest address (1FFFFh), the address

counter rolls over to (00000h). This allows the

operation to continue indefinitely, however, previous

data will be overwritten.

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DS20005142C-page 5

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