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Z80 ICE Update - Using to test for disk controller bootstrap

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  • Bill Degnan
    Today I used Bob Grieb s Z80 ICE v 0.62 to locate the bootstrap loader of a Morrow DJDMA drive controller in memory. The CPU and 64K of RAM seem to be OK, so
    Message 1 of 1 , Feb 11, 2009
      Today I used Bob Grieb's Z80 ICE v 0.62 to locate the bootstrap loader of a
      Morrow DJDMA drive controller in memory. The CPU and 64K of RAM seem to
      be OK, so the next thing to test is the drive controller. The controller
      was installed in the known-working California Computer Systems 2200
      referenced here:
      http://vintagecomputer.net/browse_thread.cfm?id=31

      This is a cool little device. I did not actually boot a disk, but at least
      now I know that the bootstrap is in the correct part of memory. I also do
      not have a working terminal without the ICE. What the ICE does is give me
      a window into the boot process, without a front panel and as I work to
      build a working system one card at a time.

      1. Removed Z80 of the Jade CPU, and in its place inserted the Z80 ICE. I
      used terminal program to read output to screen.

      2. Powered on with ICE pre-set to EA ("cpu running") mode. Status command
      (st) returns:

      0000 00 D

      0000 00 D

      0000 00 D

      INBRA Running

      3. D 0000

      message appears: "stop CPU to use that command"

      4. Q (to stop CPU)

      5. D 0000

      returns:

      00 3E 00 D3 08 C3 00 E8 etc. ("this is code for jump to E800")

      6. D E800

      returns:

      FF FF FF FF FF FF FF FF FF FF etc.

      (note that the CPU bootstrap clears the code in E800 after reading it, and
      that's why it's set to FF FF when you display it.)

      7. D 0000

      returns:

      FF FF FF FF FF FF FF FF FF FF etc.

      The bootstrap for the drive controller is supposed to be at 0038H, and it's
      not present.

      -----

      BUT

      -----

      If one repeats steps 2-7 above omitting step 6, the Jade CPU does not clear
      RAM from 0000 and the bootstrap for the drive controller IS present
      starting from 0038H (and apparently does not clear out RAM after
      displaying):

      21 4A 00 LXI H,4A

      36 MVI M,0

      7E MOV A,M

      B7 ORA A

      CA 3D 00 JZ LOOP

      FE 40 CPI 40H

      C2 3D 00 JNZ LOOP

      C3 80 00 JMP 80H

      FF DB OFFH

      I believe this code means that the bootstrap checks an 8 in. drive, then
      for a 5 1/4"

      The bottom line is that even without UART (RS232 terminal interface) I was
      able to confirm memory, z80 operation, and now the drive controller status.


      bd
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