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Cheapo IDE interface for Model 4p running MM CP/M

FireBox

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oops. :) accidents happen.

PCB looks good. pin 14 and 3 of the LS85 should be pulled high though a 1k resistor. I probably missed something but it doesn't look like the a0-a2 are connected on the schematic. If you add an LED with a resistor to Vcc you can connect the other end to DASP- line (39) on the IDE interface for an activity lite.

Scary how fast all this can be done..

Matt
 

pearce_jj

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Thanks, I added a solder-side image to the archive, which has the address lines on it.

I've not used pull-up resistors on 74LS inputs before? Good idea on the activity LED, I'll add that on.
 

FireBox

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There are actually a bunch of ports. For ide non lba mode it's like this:

Port, reading, writing (base 40h)

40,Rd data,Wr data
41,error,features
42,sector count, sector count
43,sector number, sector number
44,cyl low, cyl low
45,cyl high, cyl high
46,select head/drive, select head/drive
47,status, command

Matt
 

pearce_jj

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Try a different drive maybe? Looking at the model 4 tech ref, it seems to me there are two potential difficulties with the circuit as-is:

  • CS0 is raised coincident with IORD, but it should be selected first
  • No buffer on data bus means the IDE 3v3 logic levels could be ambiguous after travelling down two ribbon cables to get to the TRS80's internal buffer

I'm going to rework the logic a little bit. Also we can add access to CS1 (alternate status register) via A4 if that would be desirable?
 

FireBox

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I am now able to get the 5.25 WD, the 2.5 Fujitsu and the Sanddisk 1 gig CF all working. WooHoo!

I changed the 3 paralleled inverters back to one inverter. I then added an LS244 line driver and passed the output of U3B into two of the line drivers. One of the outputs of the line driver I connected to /IOR on the ide connector and the other to pin 43 (/EXTIOSEL) of the TRS80 expansion interface. The 220 ohm pull-down resistor is no longer needed.

I made this change after looking at the actual schematic for the RS 5 meg HD and noticed they were using line drivers for the /EXTIOSEL among other lines.

If I had an inverting line driver laying around I would replace the simple inverter with it negating the need for an LS04 and LS244.

A comment on the data lines...I haven't really witnessed any issue with the data, only the control lines. I guess it wouldn't hurt to buffer them.

Matt
ls244.jpgbox.jpgscreen.jpg
 

pearce_jj

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Thanks, I'm nearly done with revisions taking all of this into account. Will post back tomorrow as the routing needs completely re-doing.
 

ldkraemer

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Matt,
I'm trying to keep a copy of the Original Drawing updated with the changes from this thread. I still have some questions:

1. Do the Address Lines still need Pullup Resistors even though the signals are generated by the 74LS244 for XA0 thru XA7?
Ref: Attached 74LS244.png

2. Also I'd need to add Pullup resistors for:
XIN*
XOUT*
XRESET*
XMI*
XIORQ*

3. What gives you the ENABLE (LOW) for the 74LS244? You've skipped that enable information.
(I only show 1/2 of the 74LS244 on the updated drawing.)

Is this what you currently have wired on your Breadboard, with the exception of the Address Lines Pullup Resistors and the other signals referenced in Question 2?

I'm wondering if you can easily remove the Address Line Pullups and see if the unit still functions. Is that possible?

Thanks.

Larry
 

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Chromedome45

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What did you do with pins 1 & 19? are the outputs coming from the LS244 High or Low? If you want the outputs low tie pins 1 & 19 to ground.

LS240 is an inverting line driver. See data sheet.

I tried buffering the Data lines using an LS245 could not get 80 on port 47H actually all pins were 120. So just be advised.

LS244 data sheet: http://ecee.colorado.edu/~mcclurel/sn74ls240rev5.pdf
 
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FireBox

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Larry, for the tri-state control line I just tied it low. I tied the unused one high and grounded all the unused inputs. For the address and control lines, given they are driven with tri-state logic, I am going to leave the pull-up resistors in for the moment.

Frank, for the half of line driver you are using, tie the control pin low.

If you have an ls240 laying around its worth trying that in place of the ls04 and ls244.

Matt
 
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Chromedome45

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No I took it out. Didn't work anyway. All's I got on the ports 40-47h were 127 on each of the 8 ports. I am trying your latest mods and still that software for LDOS doesn't work. Put in 1 head and 32 tracks and it's still sitting there! Port 47h is giving 80 with this mod.
 
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