Re: Question about the speed of SPI RAM

On Mar 16, 12:25 pm, Like2Learn <like2le...@xxxxxxx> wrote:
On Mar 14, 5:26 pm, Like2Learn <like2le...@xxxxxxx> wrote:

Hi there,

We found we had to add an external RAM (SRAM or SDRAM) at the late
stage of electrical design. Basically there are only 2 GPIO pins still
available, otherwise the RAM has to share with other peripherals, such
as SPI and I2C. I prefer to connect the external RAM with SPI bus.
However, I am not sure if it is fast enough for RAM read/write. Does
anybody know the typical speed of SPI RAM read/write? Does it meet the
requirement for a device similar to an ethernet switch plus a sensor?
The data collected by the sensor is about 1K bytes per second.
Some background info: The CPU chosen is 32-bit, and can deliver 165
DMIPS at a maximum operating frequency of 100MHz.  Our application
needs 1ms time tick.

Thank you.

Has anybody know any other way to connect the RAM to the processor
with only a few IO pins, and run faster than SPI?


Your choices would include change any existing i2c memory to Ramtron
FRAM, as that can work as SRAM at moderate rates, and also as EEPROM

SPI is usually the fastest serial link, to some tens of MHz, but
there are QuadSPI devices (in Flash mainly; I think Cypress were
talking of NvSRAM in QuadSPI soon ?)

Of course, Quad SPI needs more pins (4 data lines), and a processor
with a quad capable peripheral.