DOUT short problem

[monokinetic]

Hi all,

I have all my DINX4's working for my sequencer, thanks as ever to the help here. However Im having DOUT issues now :)

Im running the DOUT tester application, I have connected one LED to the D7 connector of each 74hc595 to check each chips behaviour. The problem is that all 4 chips are lighting when I use the encoder to scroll to the D7 output. It looks pretty but not what I would expect!

Using my basic logic tester I seem to have a problem with the connection running from the pin labelled 08 on the schematic of the 1st DOUT chip to the SFR input of the next chip. It seems the connection between the core S0 and the 1st DOUT SFR pin is working fine. If I understand correctly the 08 pin of the 74hc595 is used to multiplex the chips and allow the pic to address lots of DOUT's?

But my chips seem to only have a logic signal on the 08 pin when I send the appropriate message from MIOS using the encoder. I have therefore removed all the ICs and PIC from their sockets and measured between the 08 pin and SFR pin of each DOUT and the +5v and Ground pins. This seemd to be the logical way to test for a short as found in my DINX testing! However I can find no short and the hardware behaves as described above.

Hmm any ideas anyone? are my assumptions correct?

In the meantime, happy new year ;)

I shall not expect a reply for a few days....  :D

Kind Regards

Dave mK

[TK.]

Hi Dave,

Using my basic logic tester I seem to have a problem with the connection running from the pin labelled 08 on the schematic of the 1st DOUT chip to the SFR input of the next chip. It seems the connection between the core S0 and the 1st DOUT SFR pin is working fine. If I understand correctly the 08 pin of the 74hc595 is used to multiplex the chips and allow the pic to address lots of DOUT's?

it's not really multiplexing, but just a long serial chain.

This means: MIOS shifts the data through the serial chain very quickly (within ca. 100 uS, this is hard to notice without a scope). With 16 shift registers the serial clock (SCLK) will toggle 128 times. Once each shift register has it's new state, the RCLK line will be toggled so that the new values will be transfered to the output registers.

This means also: if all LEDs are changing at the same time to the value of the first register output, then this possibly means that the shift clock line (SCLK) is not connected correctly

But my chips seem to only have a logic signal on the 08 pin when I send the appropriate message from MIOS using the encoder. I have therefore removed all the ICs and PIC from their sockets and measured between the 08 pin and SFR pin of each DOUT and the +5v and Ground pins. This seemd to be the logical way to test for a short as found in my DINX testing! However I can find no short and the hardware behaves as described above.

How about the SCLK/RCLK line? Is it connected to all ICs?

Best Regards, Thorsten.

[monokinetic]

HI TK,

thanks for the info, it helped guide me to trace the signal along SCLK and guess what, there was a short just as you suggested.  I found this last night and today I just used an encoder to skip through all 32 LEDS!!!

Thank you very much for this hint, it helped me track down the problem very quickly ;) which means now Im off to start soldering in the buttons, huarrah!!!

Kind Regards and happy new year

Dave mK