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CPU280 - No console [message #5542] Fri, 16 November 2018 05:13 Go to next message
trick-1 is currently offline  trick-1
Messages: 102
Registered: September 2016
Senior Member
Hi Folks

So I have built up the CPU280 board but have been unable to get anything out of the serial port.

When I power on the board the
- D1 goes out quickly (reset)
- D2 goes out quickly (clock frequency)
- D3 takes some time but eventually goes out (memory check)

So it looks like the CPU it talking to the ROM and also able to check the RAM.

the only other thing of note is that the CPU gets a little warm on the corner near the LED's but that's about it.

Have checked the following
- used known working null modem cable (and tried without)
- confirmed the laptop still talks to another serial device
- solder joints
- looked for solder bridges
- checked for bent pins on IC's
- Reset the DS1287 by connecting the jumper J10 with the power off.
- confirmed all parts are right location
- confirmed all parts are right value
- pulled and reseated the CPU280 - all looked OK

I am basically at the point where I am considering replacing the following
- LT1134ACN
- Z280

One other thing I might try tomorrow is obtaining a USB to Serial module and with the LT1134ACN pulled and wire it directly into pins 17/18/19/20 (TX/RX/RTS/CTS).

Anyway I thought I would see if anyone had any other suggested areas to take a look at.

Thanks in advance

Richard
Re: CPU280 - No console [message #5545 is a reply to message #5542] Fri, 16 November 2018 14:42 Go to previous messageGo to next message
lowen is currently offline  lowen
Messages: 189
Registered: August 2016
Location: Western NC USA
Senior Member
The CPU280 serial port pinout is odd. It's actually intended to go to a 25 pin connector, not a 9 pin. I'll post a pinout of my cable tomorrow.

If need be, I can send you another LT1134.


--
Bughlt: Sckmud
Shut her down Scotty, she's sucking mud again!
Re: CPU280 - No console [message #5546 is a reply to message #5545] Fri, 16 November 2018 16:25 Go to previous messageGo to next message
trick-1 is currently offline  trick-1
Messages: 102
Registered: September 2016
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Hi that would be great thank you - are you implying that the hardware description of the serial port and the pins are not quite right when it talks about 9pin? Or something else ?
Re: CPU280 - No console [message #5548 is a reply to message #5546] Sat, 17 November 2018 13:00 Go to previous messageGo to next message
lowen is currently offline  lowen
Messages: 189
Registered: August 2016
Location: Western NC USA
Senior Member
The pin descriptions are correct in the documentation, they just don't map 1:1 to a standard 9-pin plug. Here's the pin mapping I use, with the left side being the CPU280 pin header and the right hand side a male DE9 plug:
To use as a DTE (PC 9 pin male standard pinout):

CPU280 Pin -> DE9
         1 -> NC
         2 -> NC
         3 -> 3
         4 -> 5
         5 -> 2
         6 -> NC
         7 -> 7
         8 -> NC
         9 -> 8 


And then I use a null modem along with that to properly loop back all the handshaking lines. I would post a photo of the cable, but that might not help you much. It is definitely not a 1 to 1 pin correspondence, though!


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Bughlt: Sckmud
Shut her down Scotty, she's sucking mud again!

[Updated on: Sat, 17 November 2018 13:01]

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Re: CPU280 - No console [message #5549 is a reply to message #5542] Sat, 17 November 2018 13:13 Go to previous messageGo to next message
trick-1 is currently offline  trick-1
Messages: 102
Registered: September 2016
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Thanks for that - sadly (or is it fortunately) my cable represents what you have described.
So I think some thing else is going on.

I used a TTL Serial to USB adapter yesterday and connected up to the CPU side.
All I got was garbage no matter what baud I used.

The adapter has Tx/Rx lights so I could see that there was something coming out from power on and until the D3 led went out.

Will keep investigating....

Thanks again
Re: CPU280 - No console [message #5550 is a reply to message #5549] Sat, 17 November 2018 13:29 Go to previous messageGo to next message
lowen is currently offline  lowen
Messages: 189
Registered: August 2016
Location: Western NC USA
Senior Member
Ok, the other thing I've found that can cause a weird issue is if the clock is not set to x1, but is set to x2 or x4. Do you have a 'scope or logic analyzer available?

--
Bughlt: Sckmud
Shut her down Scotty, she's sucking mud again!
Re: CPU280 - No console [message #5551 is a reply to message #5542] Sat, 17 November 2018 14:30 Go to previous messageGo to next message
trick-1 is currently offline  trick-1
Messages: 102
Registered: September 2016
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Have both on the bench. Will double check. Bear in mind that the junk was with the TTL/USB adapter.
I believe I have used defaul components/crystalsas per BOM and the jumper is set to 1:1 .

Re: CPU280 - No console [message #5552 is a reply to message #5551] Sat, 17 November 2018 17:16 Go to previous messageGo to next message
lowen is currently offline  lowen
Messages: 189
Registered: August 2016
Location: Western NC USA
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Ok, let us know what you find. If your logic analyzer has the capability to do so, doing a protocol analysis of the Tx data from the Z280 UART might be informative.

--
Bughlt: Sckmud
Shut her down Scotty, she's sucking mud again!
Re: CPU280 - No console [message #5553 is a reply to message #5552] Sun, 18 November 2018 09:46 Go to previous messageGo to next message
tingo is currently offline  tingo
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Registered: February 2017
Location: Oslo, Norway
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Also note that a usb to TTL adapter might not work if this is a "real" serial port (12V levels, MAX232 compatible). Benn there, done that.

Torfinn
Re: CPU280 - No console [message #5554 is a reply to message #5553] Sun, 18 November 2018 10:30 Go to previous messageGo to next message
lowen is currently offline  lowen
Messages: 189
Registered: August 2016
Location: Western NC USA
Senior Member
Also, while I read that you had reset the DS1287, it would be worth trying a new DS12887A. The regular DS1287 or DS12887 without the A suffix isn't jumper resetable.

The fact that your LEDS are cycling correctly leads me to believe that the remainder of the board is working ok.


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Bughlt: Sckmud
Shut her down Scotty, she's sucking mud again!

[Updated on: Sun, 18 November 2018 10:32]

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Re: CPU280 - No console [message #5743 is a reply to message #5554] Thu, 13 December 2018 19:01 Go to previous messageGo to next message
lowen is currently offline  lowen
Messages: 189
Registered: August 2016
Location: Western NC USA
Senior Member
Richard, any progress on your CPU280 console?

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Bughlt: Sckmud
Shut her down Scotty, she's sucking mud again!
Re: CPU280 - No console [message #5751 is a reply to message #5743] Sun, 16 December 2018 00:44 Go to previous messageGo to next message
trick-1 is currently offline  trick-1
Messages: 102
Registered: September 2016
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So I have dropped the crystal down to the 19.6608Mhz version but no difference.
I am waiting for a new Z280 and LT1134 to turn up.
Re: CPU280 - No console [message #5765 is a reply to message #5751] Tue, 18 December 2018 07:12 Go to previous messageGo to next message
lowen is currently offline  lowen
Messages: 189
Registered: August 2016
Location: Western NC USA
Senior Member
trick-1 wrote on Sun, 16 December 2018 03:44
So I have dropped the crystal down to the 19.6608Mhz version but no difference....


The baud rate is very dependent upon the exact crystal frequency. If the frequency is off even a little, the baud rate is going to be weird.

I have an IFTools RS232 analyzer that would show this very quickly, but I would need the CPU280 in-hand to do it.


--
Bughlt: Sckmud
Shut her down Scotty, she's sucking mud again!
Re: CPU280 - No console [message #5812 is a reply to message #5542] Wed, 02 January 2019 13:57 Go to previous messageGo to next message
trick-1 is currently offline  trick-1
Messages: 102
Registered: September 2016
Senior Member
index.php?t=getfile&id=1216&private=0Hi everyone

So I have finally got the logic analyser on to the board (had to wait for an instrustar logic analyzer/osciliscope to arrive as my poor old HP1615A has suffered horizontal collapse, something else to fix).

Anyway. I thought I would start by connecting to the header (CN3) as follows
LA - CN3 - Serial Signal
CH1 - Pin 3 - TXD
CH2 - Pin 5 - RXD
CH3 - Pin 7 - RTS
CH4 - Pin 9 - CTS

Please see attached for result but it looks like there is a consistent serial signal.

CPU Crystal frequency is marked as 19.6608Mhz but when I check with the scope it shows 11.016Mhz. So I replaced the Crystal with another one from the same batch...still got the same frequncy on the scope. If I check say the 9.6Mhz Crystal this reads correctly.

So given that baud rate is dependant on CPU Frequency would be interested in where folks think to look next?

Thanks in advance
Re: CPU280 - No console [message #5813 is a reply to message #5812] Wed, 02 January 2019 14:00 Go to previous messageGo to next message
trick-1 is currently offline  trick-1
Messages: 102
Registered: September 2016
Senior Member
BTW the scope/analyzer is the Instrustar ISDS205C which is good for up to 20Mhz as a scope

http://instrustar.com/upload/user%20guide/ISDS205%20User%20G uide.pdf
Re: CPU280 - No console [message #5814 is a reply to message #5813] Wed, 02 January 2019 20:10 Go to previous messageGo to next message
lowen is currently offline  lowen
Messages: 189
Registered: August 2016
Location: Western NC USA
Senior Member
Hmm, 19.6608 MHz.... ah, I see in the hardware manual that being listed as an alternative frequency. If you have a 12MHz rated Z280 (which all of the ones I sent out are) then try a 24.576 MHZ crystal instead. Your trace looks like good serial data. Now, where are you checking the clock, right at the crystal or the Z280 clock output? The Z280 has an internal divide by two on the clock.

So, if you system is scaled on its bit rate, I would try a bit rate of either 7680, 5378, or 4303 bits per second ( those are the ratios of 9600bps to the possible clock ratios of 24.576:19.6608, 19.6608:11.016, and 24.576:11.016). The easiest to try is to put in a 24.576MHz crystal and check for 12.288MHz at the Z280 clock out on pin 47 of the Z280.

Do check to make sure the crystal can is not touching the board or has an insulator between the bottom of the can and the board, as if I recall correctly there is a via under the can.

The current CPU280 system software may not compensate for odd clock speeds, but I haven't dug deeply enough to be sure of that, since the DS1287 RTC chip can be used to figure out the clock speed.

EDIT: If you're checking the frequency right at the crystal it's possible the probe is adding enough parallel capacitance to change the oscillator frequency.


--
Bughlt: Sckmud
Shut her down Scotty, she's sucking mud again!

[Updated on: Wed, 02 January 2019 20:14]

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Re: CPU280 - No console [message #5816 is a reply to message #5542] Thu, 03 January 2019 16:18 Go to previous message
trick-1 is currently offline  trick-1
Messages: 102
Registered: September 2016
Senior Member
hmmm...was checking the clock at the crystal...probably is introducing some sort of error in measurement. If I check the Z280 clock output at pin 3 of IC4 (74HCT74) which is an easier place to find the output of pin 47 I get 9.844Mhz which is apx half the 19.6608 (although not exact).

cannot find the 24.576Mhz crystal now on the bench....grr!

I have checked the DS1287A battery, via some fine surgery, and it is showing as 2.97V so all good there. (have had to replace in too many of these DS units over the years...mainly for SUN machines). Have done the jumper reset on that again also, just in case.

I have now swapped out the Z280 (no change) and the LT1134ACN (no change)

I have tried various scaled bit rates but no joy beyond some random garbage...as a sanity check I have connected my SBCV2 board to the serial ports and it works so am confident that the PC I am using has a working serial port.

attached is a screen grab showing some more information (Frequency/Period) of the serial signal.

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