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Joules
Joined: 02 Mar 2006
Posts: 9
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| PIC18F4580 and FM25C160 |
 Posted: Wed May 17, 2006 11:28 am |
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I'm trying to use the hardware SPI and the CCS spi_read() and spi_write() functions to interface with a FM25C160 FRAM.
here's what I've got:
| Code: | | setup_spi(SPI_MASTER | SPI_MODE_1_1 | SPI_CLK_DIV_4); |
and these functions:
| Code: | void write_FRAM(FRAM_ADDRESS address, BYTE data) {
BYTE cmd[4];
BYTE i;
cmd[0] = WRITE;
cmd[1] = (address>>8);
cmd[2] = address;
cmd[3] = data;
output_low(memory_CS);
spi_write(WREN);
output_high(memory_CS);
output_low(memory_CS);
for(i=0; i<4; ++i) {
spi_write(cmd[i]);
}
output_high(memory_CS);
}
BYTE read_FRAM(FRAM_ADDRESS address) {
BYTE cmd[3];
BYTE i,data;
cmd[0] = READ;
cmd[1] = (address>>8);
cmd[2] = address;
output_low(memory_CS);
for(i=0; i<3; ++i) {
spi_write(cmd[i]);
}
data = spi_read(0);
output_high(memory_CS);
return(data);
} |
I can't detect anything happening. I try writing to an address - I can see the PIC clocking 5 bytes (WREN then WRITE op-codes, 2-byte address, byte of data), and the SDO from the PIC looks to be the correct data. I am bringing the CS high between the WREN and WRITE op-codes, as I understand is correct. When I try reading the same address I see the PIC clocking 4 bytes (the READ op-code, the 2-byte address, and the data), the first 3 on the SDO (from the PIC) are correct, but I see nothing on the SDI for the last byte.
As far as I can tell the connections are correct: /CS and /WP on the FRAM connected to the PIC, SO on the FRAM to SDI on the PIC, SI/FRAM to SDO/PIC, SCK/FRAM to SCK/PIC, /HOLD tied to +5, VDD and VSS on the FRAM connected.
Any ideas? |
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drh
Joined: 12 Jul 2004
Posts: 192
Location: Hemet, California USA
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| Posted: Wed May 17, 2006 11:48 am |
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What about the /WP line?
_________________
David |
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Joules
Joined: 02 Mar 2006
Posts: 9
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| Posted: Wed May 17, 2006 12:54 pm |
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/WP line is tied to a pin on the PIC which I'm holding high (maybe I've just been looking at this too long, /WP is active low and prevents writes, is that saying if it's high it allows writes?).
If I'm reading the datasheet correctly it doesn't seem like it should matter anyhow, since /WP only prevents writing to the status register, not memory.
Thanks though! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed May 17, 2006 1:08 pm |
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I would try using SPI Mode 0 because apparently Ramtron made
an older chip (FM25160) that doesn't support Mode 3. What if you somehow got the older chip ? It's safer to use Mode 0.
Also, this chip has internal block write protection bits in the Status
register. Have you enabled this by accident ? |
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Joules
Joined: 02 Mar 2006
Posts: 9
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| Posted: Thu May 18, 2006 8:26 am |
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thaks for your help, I tried SPI_MODE_0_0, no luck there, I also tried adding this:
| Code: |
output_high(memory_WP);
output_low(memory_CS);
spi_write(WREN);
output_high(memory_CS);
delay_cycles(8);
output_low(memory_CS);
spi_write(WRSR);
spi_write(0);
output_high(memory_CS); |
which I believe should set the block protection to none, and I still get nothing on the SO of the FRAM when I run the read function, though I really have no idea if the writes are working or not (it's possible that the write isn't working but the read is, but I'm getting 0 back because I never wrote anything to the memory, correct?).
I'm almost thinking bad chip - if it where a DIP I'd just try another one, with SOICs I want to be pretty sure before I swap. |
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Joules
Joined: 02 Mar 2006
Posts: 9
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| Posted: Thu May 18, 2006 8:37 am |
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Got it working; just messing around with the setup_spi() function, I added SPI_SAMPLE_AT_END and it appears to be working.
thanks again for the help. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu May 18, 2006 1:33 pm |
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What is the oscillator frequency on your PIC ?
I'd like to analyze the timing and find out why the sample-at-end
feature had to be enabled. |
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Joules
Joined: 02 Mar 2006
Posts: 9
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| Posted: Fri May 19, 2006 4:14 am |
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oscillator is 16MHz.
I've also got an MCP4921 DAC using the SPI, that's not connected to the PICs SDI however. |
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