SPI serial EEPROM without chip select?

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Astrid

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Hello,
my supplier have not seriel SPI EEPROM for 2 line SPI (Bidirectional Data line) and I have last three line for comunnication with EEPROM.
EEPROM is sole chip on SPI bus, MCU is STM32F103. EEPROM is M95128-W
is possible and problem free solution connect CS direct to GND and use three line for SCLK, SI a SO?
 

my supplier have not seriel SPI EEPROM for 2 line SPI (Bidirectional Data line) and I have last three line for comunnication with EEPROM. EEPROM is sole chip on SPI bus, MCU is STM32F103. EEPROM is M95128-W
Click to expand...
What I understood,from this,is that you intend to use two lines for SPI,but in the EEPROM,you have 3 lines.That is correct,right?
 

You cant just ground them, In EEPROMs They are not only used for chip selection but also for data synchronization.

They are also used to denote end of a read or write cycles.

So that will cost you one more GPIO line.
 

2-line interface would use I2C, e.g. M24M01. Sharing one line for MISO and MOSI would work with SPI EEPROMs as well, but is more difficult to handle at the procesor side. CS control is mandatory, as explained by Venkadesh.
 

I have a little problem in the exact expression in English
It is simple, I have only three free MCU PIN
1. SPI Clock
2. SPI Bidirectional data
3. CS, Chip Select
but for example this EEPROM
is for full Duplex SPI
1.SPI Clock
2.SPI Data Out
3.SPI Data In
and because for CS is not free PIN and EEPROM is on SPI single.
I want to give CS permanently to 0.
The question is whether it will be problematic solution?
 

You can see from the datasheet that the EEPROM is tristating MISO while receiving data. In so far, common MISO/MOSI line is definitely an option. It's also supported by STM32F1xx, see "Configuring the SPI for simplex communication" in reference manual.

I don't know if your pin map still allows to use the respective dedicated SPI pins, otherwise use bit-banging SPI, it has no problems with birectional data line anyway.
 

MISO is in high impedance state when not in use, so you can just short the MISO and MOSI of EEPROM and interface with the bidirectional SPI pin.

So you can keep using the CS pin.
 

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