ESP8266 Community Forum

- Mon Nov 07, 2016 6:41 am #57758 From the data sheet: "The Microchip Technology Inc. 47L04/47C04/47L16/47C16 (47XXX) is a 4/16 Kbit SRAM with EEPROM backup. The device is organized as 512 x 8 bits or 2,048 x 8 bits of memory, and utilizes the I2C serial interface. The 47XXX provides infinite read and write cycles to the SRAM while EEPROM cells provide high-endurance nonvolatile storage of data. With an external capacitor, SRAM data is automatically transferred to the EEPROM upon loss of power. Data can also be transferred manually by using either the Hardware Store pin or software control. Upon power-up, the EEPROM data is automatically recalled to the SRAM. Recall can also be initiated through software control."

The 47C04 solves a tricky problem for me where one of my projects needs nonvolatile storage that has to be updated once each second.

The Lua script requires the firmware with the I2C module and assumes all arithmetic is done using integers only.

Code: Select all-- functions for accessing Microchip 47L04/47C04/47L16/47C16 I2C Serial EERAM

-- Status Register:
--bit 7 AM: Array Modified bit
--      1 = SRAM array has been modified
--      0 = SRAM array has not been modified
--bit 6-5 Unimplemented: Read as ‘0’
--bit 4-2 BP<2:0>: Block Protect bits
--      000 = Entire array is unprotected
--      001 = Upper 1/64 of array is write-protected
--      010 = Upper 1/32 of array is write-protected
--      011 = Upper 1/16 of array is write-protected
--      100 = Upper 1/8 of array is write-protected
--      101 = Upper 1/4 of array is write-protected
--      110 = Upper 1/2 of array is write-protected
--      111 = Entire array is write-protected
--bit 1 ASE: Auto-Store Enable bit
--      1 = Auto-Store feature is enabled
--      0 = Auto-Store feature is disabled
--bit 0 EVENT: Event Detect bit
--      1 = An event was detected on the HS pin
--      0 = No event was detected on the HS pin

-- read a byte from status register
function readStatus()
   i2c.start(id)
   i2c.address(id,0x18,i2c.RECEIVER)     -- 0x18 is control register
   data=i2c.read(0x00,1)                 -- 0x00 is address of status register
   i2c.stop(id)
   return data
end

-- write a byte to the status register
function writeStatus(data)
   i2c.start(id)
   i2c.address(id,0x18,i2c.TRANSMITTER)   -- 0x18 is control register
   i2c.write(id,0x00)                     -- 0x00 is address of status register
   i2c.write(id,data)
   i2c.stop(id)
end

-- enable the EERAM auto store function
function EnableAutoStore()
   writeStatus(0x82)
end

-- write a byte to the command register. The COMMAND register is a write-only register that allows the
-- user to execute software-controlled Store and Recall operations.
function writeCommand(data)
   i2c.start(id)
   i2c.address(id,0x18,i2c.TRANSMITTER)   -- 0x18 is control register
   i2c.write(id,0x55)                     -- 0x55 is address of control register
   i2c.write(id,data)
   i2c.stop(id)
end

-- The Software Store command initiates a manual Store operation.
function Store()
   writeCommand(0x33)
end

-- The Software Recall command initiates a manual Recall operation.
function Recall()
   writeCommand(0xDD)
end;

-- write bytes (data) to sequential SRAM locations starting at 'address'.
function writeSRAM(address,data,...)
  local arg={n=select('#',...),...}
  i2c.start(id)
  i2c.address(id,0x50,i2c.TRANSMITTER)          -- 0x50 is SRAM register
  i2c.write(id,address/256,address%256,data)    -- write address high byte, address low byte, first data byte
  for i = 1,arg.n do i2c.write(id,arg[i]) end   -- write sequential data bytes
  i2c.stop(id) 
end

-- read a byte from SRAM location 'address'
function readSRAM(address)
   i2c.start(id)
   i2c.address(id,0x50,i2c.TRANSMITTER)         -- 0x50 is SRAM register
   i2c.write(id,address/256,address%256)        -- address high byte, address low byte
   i2c.stop(id)
   i2c.start(id)
   i2c.address(id,0x50,i2c.RECEIVER)            -- 0x50 is control register
   data=i2c.read(0x00,1)                        -- 0x00 is address of status register
   i2c.stop(id)
   return data
end

-- zero all SRAM locations
function clearSRAM()
   for high=0,0x07 do
      print("page 0x"..string.format("%02X",high))
      tmr.wdclr()
      for low=0,0xFF do
         writeSRAM((high*256)+low,0)
      end
   end
end

-- print the contents of the status register as two hex digits
function printStatus()
   print("0x" .. string.format("%02X",string.byte(readStatus())))
end;

-- print the contents of a SRAM location as two hex digits
function printSRAM(addr)
   print("0x" .. string.format("%02X",string.byte(readSRAM(addr))))
end

-- initialize i2c for the EERAM
sda=6 -- pin 5 on 47C04 connected to GPIO12 of the EPS8266 ESP-12
scl=5 -- pin 6 on 47C04 connected to GPIO14 of the EPS8266 ESP-12
id =0  --always zero
i2c.setup(id,sda,scl,i2c.SLOW)