Serial SRAM is a standalone volatile memory that offers designers an easy and inexpensive way to add more RAM to their application. These 8-pin low power, high performance SRAM devices have unlimited endurance and zero write times, making them ideal for applications involving continuous data transfer, buffering, data logging, audio, video, internet, graphics, and other math and data-intensive functions. These devices are available from 64 Kbit up to 1 Mbit in density and support SPI, SDI and SQI™ bus modes.
Serial NVSRAM offers non-volatile RAM storage and is ideal for applications that need to write very often to the memory. This device is significantly lower cost than other non-volatile RAM devices and the data is backed using an external battery. This 8-pin, SPI device supports unlimited instantaneous writes to the memory array, making it ideal in applications such as meters, data loggers, data recorders, black boxes. These devices are available in 512 Kbits and 1 Mbit densities.
Getting Started with Serial SRAM
Microchip’s Serial SRAMs offer an easy and inexpensive way to add RAM to an application. With small, 8-pin packages and the SPI interface (which only requires 4 I/Os) these devices give designers added flexibility with regard to their RAM needs. The Serial NVSRAM devices offer the industry’s least expensive non-volatile SRAM or FRAM solution. These low power NVSRAM devices offer unlimited, instantaneous writes to the memory array while automatically backing up data in the event of a power shutdown using an external battery.
RAM Expansion Options:
There have traditionally been two ways to increase an application’s RAM:
- Use a larger microcontroller. This option is less attractive if you must buy a larger, more expensive micro just to get more RAM.
- Use external parallel RAM. But, parallel RAM uses large packages and typically requires at least 16-20 I/Os.
Serial SRAM now offers the flexibility to add RAM to a design without the disadvantages of a large micro or parallel RAM and uses the simple 4-pin SPI interface. These devices also offer improved performance with the SDI and SQI interface that offers up to a 4x improvement in data rates.
Serial SRAM Bus Modes – SPI, SDI and SQI
Serial SRAM devices are designed to work on the standard SPI interface at 20 MHz. On the 512 Kb, 1 Mb devices – the SO, SI (pin 2, pin 5) along with SIO2, SIO3 (pin 4, pin 7) are designed to work as bi-directional I/O pins.
In SQI mode, all 4 pins (pins 2, 4, 5, 7) are configured to read or write at any given time effectively ensuring 4 bits are transferred across the bus in a single clock cycle – this, in effect, multiplies the data rate by 4. So for example, a task that takes 40 clock cycles to complete in standard SPI mode can now be completed in 40/4 = 10 clock cycles. This feature is extremely useful when large amounts of data need to be transferred quickly.
In SDI Mode, only 2 of the pins are configured as bi-directional I/O pins (pin 2, pin 5), allowing you to get a maximum of 2x data rates. Our standard 512 Kb and 1 Mb SRAM devices can be used in SDI and SQI modes.
The same device in the same footprint can be used for SDI and SQI.
Serial SRAM Family
Serial NVSRAM Family