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RE: [N8VEM-S100:4627] 8080 CPU - 2nd Mod required

Hi Guys,

Ok, I just finished building my board and found another error.
Apparently I didn't do a good job at entering the 8T97 (74LS367) chip.
Pin 15 was left disconnected. 
Please install 1 jumper from IC H7 (8T97) pin 15 to IC H6 (74LS04) pin 2.

Alternatively, you can hide this jumper under IC H7 by placing it between pins 15 and pin 1.

It's a shame I didn't catch this error, the trace rights right beside Pin 15.  I suppose
you could scratch the solder mask and make the connection there at pin 15 with a glob of solder..

The HEAT is ON....

Also, I have been trying to use as many older vintage chips on my board
and this drives the current up and the regulator is getting hot.
I let mine run open air for 30 minutes and the regulator reaches 80c.

If 82C50's or 16450's/ 16550's are used, this will reduce the current
I tried with 16450's and removed 2 1489's for modem control.
This brought the temperature down to about 70c

On my prototype board, the temp is about 60c
It's using newer chips.

The +8V line on my IMSAI is measured at 8.9V so this will also
contribute to the heat.  I think 7V is the rated minimum voltage for the 7805.

I wonder if I should add a diode in there to drop it a little?

Firmware...  almost there.  The boot strap can now load the CP/M sectors in from the file, the jump table is in the right place and I think the functions are working...  but it's still not working.  I'll need to take a break and come back to this next week.

Josh Bensadon

From: crus...@hotmail.com
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:4627] 8080 CPU - UARTS Tested
Date: Fri, 18 Jul 2014 09:32:28 -0400

Hi Guys,

Fabio asked if the board could use other UART chips, namely the 16550 chip.

I don't see why not, they are suppose to be pin compatible and should be backward compatible register sets.
But I decided to test it out quickly for sake of knowing for sure.  On a quick test (ie can I send and receive data),
they all work.  Here's a list of chips from my junk box that I've tested:

NS: PC8250CN
WD: WD8250-PL
WD: 8250B-20
SIS: 82C50B

SIS: 82C450
NS: NS16450N
NS: PC16550DN

I suppose the hardware flow control and modem controls would all work the same, but I'm not using any of that.

Bah, flow control is for 8008 users!  Here we are using an 8080A chip. 2Mhz and 64K of memory ought to be enough for anybody.


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