I'm designing a test/loopback board for a laser controller. I went to engineering school for five years for this?
Anyway, I need to verify the SPI interface on the DUT; it comes out on a ribbon cable for our customer to use. I was thinking that I could put the dumbest, easiest to program SPI part in the world on my test board, and let the uP in the DUT pound on it to verify the link. So, what's the dumbest SPI chip on the planet?
-- John Larkin, President Highland Technology, Inc
spi input or spi output ??
spi does not come without a peripheral or a cpu attached.
So you need an spi output .... right ?
The spi talks to ..... what ?
spi can be so many thing it is impossible to say.
4 wires? 3 wires? data on rising/falling edge of clock? minimum time from enable to clock? minimum time from last clock to ! enable? turn around from input to output on data? number of bits per read/write? to mention somefigure out what it needs to talk to and simulate that with what ever fpga/cpld board you have around
-Lasse
I'd say, if you're familiar with them, that one of the PICs is about as easy as it gets. We use these for quick and dirty test interfaces around our labs:
What about an SPI relay driver?
Use the outputs to blink some LEDs, or something.
A 74HC595 shift register and 8 LEDs with resistors.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant
The board I'm trying to test has an ARM processor with an SPI port: MISO, MOSI, ChipSelect, SPIclock, all brought out on a ribbon cable. I need to test that port, so I need a target device.
-- John Larkin, President Highland Technology, Inc
How about a 25AA010AT 128x8 SPI EEPROM? Write and verify. SOT-23-6. Sells for 30 cents or so.
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com
74HC595? I think the Clk needs to be inverted to make it compliant. Hang some LED on the outputs and watch them flicker?
Or NXP has some LED/Peripheral drivers that are SPI/I2C
Or maybe these are too Dumb.
Cheers
DOS and bit banging the parallel port.
The only disadvantage I see with the 74HC595 is that it doesn't have a MISO pin, so there's no way to verify that that component of the protocol is working correctly.
I need something I can write to and read back from, to test all four SPI port lines.
I could loop MOSI to MISO; we verified that the ARM will talk to itself that way, but that doesn't test chip select or clock integrity, and MISO could be shorted to MOSI on the DUT board, and we'd miss that. Policy is that a production test should catch all reasonably possible opens/shorts/bad parts/assembly errors.
Maybe I'll just use an SPI eeprom, and write a 16-bit test pattern then read it back. That would test the entire port, but that is a mild nuisance to program. But then, I don't have to write the code!
The HC595 works if I shift 16 bits in and out and manually read the LEDs, but that's not as automated as it might be.
-- John Larkin, President Highland Technology, Inc
The shift register does have input and output available, so I could test MISO/MOSI/CLOCK. But not CS, except by eyeballing LEDs.
-- John Larkin, President Highland Technology, Inc
Oh right, I forgot about the daisy chaining output.
No, it's the other way: the DUT has an ARM with a master SPI port, and I need a target devive to prove that the SPI port works. I want to put that on my test board.
-- John Larkin, President Highland Technology, Inc
Yeah, I might just use an EEPROM. We have SO8's in stock, AT93C86A. It's a little messy to program, but not too bad.
-- John Larkin, President Highland Technology, Inc
Aren't they Microwire rather than SPI?
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com
You can daisy chain them--put SDO to MISO.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant
even easier then, just configure the pins as GPIO in the test program and test the connections that way
-Lasse
Do you have complete control of the SPI interface? How about a dual D-FF? Connect D1 to MOSI, SCK to Clk1, Q1 to D2, SS to Clk2, and Q2 to MISO; a 1-bit SPI port.
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