Dragon 32/64 Disk Controller Card

This project contains the design and build documents for a recreation of the DragonDos disc controller

Design

The schematics use a WDC WD2797 disc controller IC as the core of the board, this is consistent with the original DragonData design. Other 2797 ICs from different manufacturers should still work

Other than the rom and controller the discrete logic chips are surface mount to help with the availability of components. In all cases the surface mount parts are of the largest versions available to try and make the assembly of the board feasible for hand soldering

Progress

In the current state the board is untested

The PCB layout is (very) generous on dimensions and needs work to shrink it down. Iterating on this won't change the functionality and should significantly reduce the size of the board, and hence the cost of fabrication

Assembly and BoM

Until the board progresses to a point where it can be tested the assembly instructions and the proven bill of materials are left unpublished

Calibration

1. Adjust the RPW timing - measure the pulse width of the TG43 signal from pin 29 on U2. Use R10 to fix the pulse at 600ns

2. Adjust the WPW timing - measure the pulse width of the signal from pin 3 of U6, pin 31 of U2, or pin 22 of the IDC connector (the IDC pin is inverted). Use R9 to fix the pulse at 300ns

3. Adjust VC0 timing - measure the frequency of the DIRC signal from pin 1 of U6, pin 16 of U2, or pin 18 of the IDC connector (the IDC pin is inverted). Use C3 to set the signal at 250KHz

Complete Adjustment Procedure

The official documentation identifies a more complex and thorough adjustment procedure. Where !TEST is referenced you can use the test point on the board at J1. Pin 1 is connected to !TEST on U2 (pin 22)

Write Precompensation

1. Set !TEST to high (1)
2. Strobe !MR on U2 Pin 19
3. Set !TEST to low (0)
4. Measure pulse width on U2 Pin 31
5. Adjust R9 until pulse width is 300ns
6. Set !TEST to high (1)

Data Separator

1. Set !Test to high (1)
2. Strobe !MR on U2 pin 19
3. Check that !5/8 and !DDEN are set properly. U2 pin 17 and 37
4. Set !TEST to low (0)
5. Measure pulse width on U2 Pin 29
6. Adjust R10 until pulse width is 600ns
7. Measure frequency on U2 pin 16
8. Adjust C3 until frequency is 250KHz
9. Set !TEST to high (1)