Jupiter Ace Hardware RFL Home built Ace

RFL Ace - Home built.

upiter Ace's can be hard to get hold of but if you are a Forth fan and like the Ace then you can always build your own, like Ricardo Fernandes Lopes did. Ricardo is big Ace fan and prolific Ace Forth programmer with many programs to his name such as, WRD, DIVN, Calendar, Towers of Hanoi, SokoACE, SokoEd, Ace Mines, FontEd and we hope many more! He has also helped the archive site out with many other items such as his Reference Card, screen layout card, Tape file format and others including the translations of Spanish Ace Forth magazine articles to be added in to the archive soon.

These are the differences from the original Ace circuit:

My 60Hz mod [details below].
A 128k RAM IC (using only 52k) The first 4k addresses are not overlapped in 1k block as in the original Ace.
2x 2k RAM ICs in the video section (using only 1k of each one).
Clock generation using logic gates instead of transistor.
A different video combiner (simple and works well!).

I've not built in the expansion edge connector port, video expansion port, and the tape in and tape out connectors are implemented. It's not compatible with AMI at the moment because of the use of a single RAM IC, I will solve this soon.

60 Hz video Hardware changes:

Crystal changed from 6.500 MHZ to 6.552 MHz.
Z20A, Z21A & Z21B gates connections re-configured as follows
          ____
CNT 10---|    \
CNT 11---|Z21B |---- Reset line counting (pin 2,12 of Z11 and pin 12 of Z10)
CNT 17---|____/
          ____
CNT 14---|    \       ____
CNT 15---|Z21A |-----|    \
CNT 16---|____/      |Z20A |--- FIELD (pin 12 of Z19 and pin 6 of Z25)
          ___     +--|____/
CNT 12---\   \    |
          |   >O--+     <--- Additional NOR gate
CNT 13---/___/

IMPORTANT!
pin 12 of Z10 disconnected from ground and connect as indicated above!

The spare 3 gates of the additional 74LS02 (4 NOR gates) can be used to replace the
transistor based oscillator (Q1) and CPU clock inverter (Q2).

-----------------------------------------------------------------------
                     ______        ______
VIDEO               |      |      |      |
CLOCK: 6.552 MHz -->| /416 |--+-->| /262 |--> FIELD  VSync: 60.11 Hz
                    |______|  |   |______|
                              +-------------> LINE   HSync: 15750 Hz

-------------------------- One Video Line -----------------------------

VIDEO CLOCK COUNTING: 416 clocks (Same as original 50 Hz version circuit)

VIDEO LINE TIMING: 63.49 us (15750 Hz) 
 ___________________________________________________________________
| 64 counts |           256 counts          | 64 counts | 32 counts |
|  9.768 us |            39.07 us           |  9.768 us |  4.884 us |
| L margin  |      32 character columns     | R margin  |   HSYNC   |
|___________|_______________________________|___________|___________|
            V
       COUNT-START->

-------------------------- One Video Frame -----------------------------

VIDEO LINE COUNTING: 262 raster lines (Same as Edwin's Accurate mod)
__________________________________________________________________________
           |          CNT bits          |
LINE count | 17 16 15 14 13 12 11 10  9 | Remarks
___________|____________________________|_________________________________
  0 (+192) |  0  0  0  0  0  0  0  0  0 | Line counting start
192 ( +32) |  0  1  1  0  0  0  0  0  0 | Bottom margin start
224 (  +8) |  0  1  1  1  0  0  0  0  0 | Bottom margin end, V Sync start
232 ( +30) |  0  1  1  1  0  1  0  0  0 | V Sync End, Top margin start
262        |  1  0  0  0  0  0  1  1  0 | Top margin end, Reset counters
___________|____________________________|_________________________________

VIDEO FRAME TIMING: 16.64 ms (60.11 Hz)
 ___________________________________________________________________
|  30 lines  |           192 lines           |  32 lines  | 8 lines |
|  1.905 ms  |            12.19 ms           |  2.032 ms  | 507.9 us|
| Top margin |         24 text lines         | Bott margin|  VSYNC  |
|____________|_______________________________|____________|_________|
             V
        COUNT-START->


The circuit will work correctly if using the original 6.500 MHz crystal
but the timing will be slightly different.

VIDEO LINE  TIMING: 64 us    (15625 Hz) (same as the original circuit)
VIDEO FRAME TIMING: 16.77 ms (59.64 Hz) (same as the Accurate Mod by Edwin Blink)

Ricardo has kindly made his schematic available for download there are 5 pages in PDF. The schematics have been created using kiCAD because it allowed him to have more then one sheet in a project.