Re: [N8VEM: 14618] SBC V2 build not working

Flash chip enable should go low to enable the Flash.
2.5 V is not low and will not enable the Flash.

This is not a valid logic level. Could this signal be shorted
to one that is sitting high?

Bob

From: Douglas Goodall <dougl...@mac.com>
To: n8...@googlegroups.com
Sent: Monday, September 10, 2012 10:29 AM
Subject: Re: [N8VEM: 14618] SBC V2 build not working

Wayne,

I have responded to questions I understand, and included a photo of my working board.

If you are fighting only the serial link (it happens), you could check for wiggles on the 16550 TX pin.

The MAX232 comes in several varieties, and some need the .1uF capacitors for the charge pump

and some use 1uF caps instead, check the datacheet for your RS232 evel converter.

On Sep 10, 2012, at 5:27 AM, opticpow <wa...@ingram.net.au> wrote:

Hi Doug,

I've posted pics to here

I've got the scope out and done some probing. I've uploaded some scope captures with the board pic above.

The scope images are very cool :-)

I have CPU & UART clock

Is the CPU clock making it to the CPU chip clock input?

Flash A0 is pulsing at 1mhz
CPU reset is at 4.5v. should this be at 5v?

I believe this is ok.

CPU IORQ is high

This seems odd to me. When the firmware is running, it makes I/O calls to the UART to output characters through the

serial port. It also should be polling the UART for console input.

CPU MREQ is pulsing @4hmz

This could be OK depending on what your CPU clock is at

CPU WAIT & BUSRQ are both at 3.9v. Should this be 5v??
while reset button is pressed, RESET drops to 200mv
Flash CE is pulsing between about 2.5v & 5v @ 4mhz (see pic). Not sure this is right??

This scope image looks bizarre to me. I would expect a cleaner looking signal than this.

Are you sure the scope was set right for this capture?

Flash OE is pulsing at 2mhz

This could be ok

RAM A0 pulsing @ 1mhz
Where abouts do I find the short loop images. I've had a browse on the files section and could not find them.

I can't find them either. They were part of Andrew's initial BIOS efforts and I cannot find any of those files.

Lets ask Andrew where we can find them, or can he post them to the wiki where we can find them.

What kind of computer are you using for system development? (to build the rom image from sources)

Here is the link to a good document on jumper settings. My serial handshaking lines are opposite of yours.

Sorry I cannot give you definitive answers about voltage levels.

http://n8vem-sbc.pbworks.com/w/page/39172478/N8VEM%20SBC%20V2%20Jumper%20Settings

Thanks,
Wayne.

On Monday, September 10, 2012 8:14:29 AM UTC+10, douglas_goodall wrote:
Wayne,

Here are a few steps I follow. (Some of which you have already done...)

1. Verify power on all +5 pins
2. make sure CPU oscillator is wiggling
3. Make sure clock input to CPU is wiggling
4. Make sure A0 on the flash is wiggling, maybe CE and OE as well
5. Make sure clock input to UART is wiggling
6. See if Tx pin on UART is wiggling after reset, if so serial wiring is likely the problem
7. Use low level test images with short loops (also known as scope loops)
8. When doing low level probing , if a signal is not doing what you expect you may have a problem
where the socket pin does go into the hole, but for some reason solder hasn't reached it, reflow it and check again
(test for continuity between chip lean and trace underneath the board. I have found some of these).

It is possible to have a bad chip. The bottom line if following the basic functions...
CPU clock is running, EEPROM is reading (if not maybe problem with I/O decoder) Check enabled on I/O devices

These are my major thoughts. Be brave, we have all been through this difficult moment and most have working boards now.
You learn a lot in this phase if you engage it enthusiastically.

Regards,

Douglas

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