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PCF2127 clock IC RAM write/read

 
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donW



Joined: 12 Apr 2015
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PCF2127 clock IC RAM write/read
PostPosted: Sun Apr 12, 2015 3:20 pm     Reply with quote
I am trying to write & read to the RAM in the PCF2127 clock IC
using SPI.
The data sheet only shows the IIC sequence.
I can wr/rd the clock date & time and the configuration regs OK, so my hardware is good.

Has anyone done this?
PCM programmer



Joined: 06 Sep 2003
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PostPosted: Sun Apr 12, 2015 4:00 pm     Reply with quote
It's shown in Figure 38b on page 64 of the pcf2127 data sheet.
www.nxp.com/documents/data_sheet/PCF2127.pdf
The diagrams on the lower 2/3rd's of the page show how to do it.
Compare the code below to the diagrams.
Code:

void write_pcf2127_ram(int16 addr, int8 data)
{
output_low(PCF2127_CS);
spi_xfer(0x3a);
spi_xfer(addr > 8);  // addr msb
spi_xfer(addr);      // addr lsb 
output_high(PCF2127_CS);

output_low(PCF2127_CS);
spi_xfer(0x3c);
spi_xfer(data);
output_high(PCF2127_CS);
}

The code above is for writing one byte only. The diagrams show how
to write multiple bytes. In that case you would supply a pointer to an
array. The function above would have to be re-written somewhat.

The reading of RAM is shown on page 65. You can write that one.
donW



Joined: 12 Apr 2015
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PostPosted: Sun Apr 12, 2015 4:19 pm     Reply with quote
thanks for quick reply!
my 'write byte' is in the same sequence as you show.
Can you show me the 'read a byte' code?
The datsheet IIC routine is confusing: it shows to setup the read adress,
then a write to reg 1D ? then data read....
donW



Joined: 12 Apr 2015
Posts: 6
Location: New Zealand

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PostPosted: Sun Apr 12, 2015 4:43 pm     Reply with quote
your datasheet is newer than mine.. which does not have the SPI examples
I am doing write & read as per your datasheet, but still can only get 00's back from the RAM...
donW



Joined: 12 Apr 2015
Posts: 6
Location: New Zealand

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PostPosted: Sun Apr 12, 2015 5:15 pm     Reply with quote
Found my problem ! my write routine was using the wrong port for /CS pin..
ram now working...
Thanks for the newer version of datasheet..
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