Atmel AT45D0xx dataflash with the BASIC Stamp

Atmel dataflash memory is attractive for use with the BASIC Stamp in data logging or other memory intensive applications.

• It is available with lots of memory in a small package, from 128 kbytes up to 512kbytes in an 8 pin soic.
• Cost per byte much lower than eeprom.
• The serial SPI interface requires only 4 control lines from the Stamp.
• Dataflash has a couple of rather large RAM buffers (from 264 to 528 bytes), which can be used as a convenient extension of the Stamp's limited RAM. The RAM buffers are there to support the high data transfer rates that are required by speed or photo recording. When a RAM buffer is full, its entire contents can be transferred to a page of flash memory. While the transfer is taking place (which takes several milliseconds), data can continue to flow at high speed into the second RAM buffer.
• It has an feature-rich command set that allows many modes of access to the flash and to the RAM, without being as complicated and protocol intensive as some other memory standards.

Here is a simple getting started demo of some of the main commands required to access the RAM memory and to program and read the flash memory .

   
' Demo of the AT45D0xx
' under control of the Stamp II
' (c) 1999 Tracy Allen, Electronically Monitored Ecosystems.
cmd  var byte  ' AT45D0xx command, to be sent by the Stamp
page var word  ' page of 264 bytes, 1024 pages in the AT45D020
adrs var byte  ' which byte on page
               ' bytes 256-263 not used
ix   var byte  ' general purpose index
x    var byte  ' general purpose byte
   
' here are the connections to hardware control lines:
atcs con 8     ' AT45D0xx chip select line
sck  con 9     ' AT45D0xx clock line
sdo  con 10    ' AT45D0xx data output line
sdi  con 11    ' AT45D0xx data input line
sdip var in11  ' AT45D0xx data status
   
' here is demo data that will be stored in the dataflash:
msg  data "this is a test.. 1.. 2.. 3.."
   
outs=%0000000111100001
     'fedcba9876543210
dirs=%1111011111111111
   
main:
  '------------------------------------------------
  ' first write some data to one of the RAM buffers
  cmd=$84   ' write to buffer 1 command
  adrs=0    ' write at the beginning of the page
  gosub sndcmd
  for ix=0 to 27  ' 28 byte message
  read msg+ix,x   ' read it from BS2 eeprom
  debug x         ' show it on screen
    shiftout sdo,sck,msbfirst,[x\8]   ' put it in the AT45D0xx
  next
  debug cr       
  high atcs       ' finish the command
'
  '------------------------------------------------
  ' now read back the data from the RAM buffer
  cmd=$54   ' read from buffer 1
  adrs=0    ' read from the beginning of the page
  gosub sndcmd
  for ix=0 to 27  ' 28 byte message
    shiftin sdi,sck,msbpost,[x]   ' get it from the AT45D0xx
    debug x         ' show it on screen
  next
  high atcs       ' finish the command
  debug cr
'
  '------------------------------------------------
  ' now erase a flash eeprom page and put the data there
  cmd=$83    ' erase flash page & write buffer 1 there
  page=5     ' choose page 5 for the demo
  debug hex4 page,cr
  gosub sndcmd     ' do it, erase and program page 5!
  high atcs        ' finish the command
  gosub waitready  ' wait for it to finish writing
  'pause 20    ' alternative to wait routine, hard pause
'
  '------------------------------------------------
  ' now read data directly from the flash page
  cmd=$52  ' read page direct command
  page=5   ' same page as above
  adrs=0   ' top of the page
  gosub sndcmd
  for ix=0 to 27   ' read 28 bytes
    shiftin sdi,sck,msbpost,[x\8]
    debug x
  next
  high atcs   ' finish the command
  debug cr,cr
'
pause 1000
end   ' end of the demo program
   
'------------------------------------------------
' subroutine sends the command
' some commands require more bytes than others
' some commands require a lot of extra clocking bits
' This routine asserts chip select, but it is up to the
' calling routine to bring the chip select back high.
sndcmd:
  low atcs
  shiftout sdo,sck,msbfirst,[cmd\8,page<<1\16,adrs\8]
  if cmd>$56 then sndend
  shiftout sdo,sck,msbfirst,[0\8]
  if cmd>$52 then sndend
  shiftout sdo,sck,msbfirst,[0\16,0\8]
sndend:
  return
   
   
'------------------------------------------------
' subroutine waits for the chip to finish writing to flash page
' it has a timeout loop
' note that it is necessary to wait before starting another
' write to the flash
' however, the program could start sending data to the 
' alternate RAM buffer #2 even while the write is in progress.
waitready:
 low atcs
 shiftout sdo,sck,msbfirst,[$ae\9]
 ix=255
wr1:
pause 1
 ix=ix-1
 if sdip-1*ix then wr1
 high atcs
 if ix=0 then error
return
   
error:
 debug "dataflash write error",cr
return

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