CRT display is controlled by the CRTC integrated circuit. All signals are digital TTL levels (0-5V), which are then interpreted by the CRT HV driver board.
| # | signal | color |
|---|---|---|
| 1 | NC | |
| 2 | GND | black |
| 3 | NC | |
| 4 | PIXELS | brown |
| 5 | NC | |
| 6 | NC | |
| 7 | VSYNC | violet |
| 8 | HSYNC | gray |
| 9 | NC | |
| 10 | GND | black |
| 11 | CONTRAST | green |
| 12 | CONTRAST | blue |
| signal | value |
|---|---|
| Vertical Sync | ~20 ms |
| Horizontal Sync | 53 us |
| Lines | 370 lines |
| Pixel Clock | 15MHz (XTAL3) |
These signals are not compatible with a common PAL TV-set monitor, neither the voltages nor the timings. If you want to use an external monitor, some circuit with frame buffering capabilities is needed. See below.
Being the real-time chip which handles the image on the screen, the CRTC has higher priority in accessing the video RAM, and can temporarily halt the Z80 CPU when they both try to access it.
Example performance test code:
_performance_test:
in a,($A0) ; toggle CRTC /CS
; used just to measure the spike
; and determine the cycle loop
; with an oscilloscope
ld de,$0100 ; repeat cycle 256 times
loop:
ld a,($2000) ; read from normal memory or video memory
; takes 13 cycles for normal memory
; takes ~15 cycles for video memory
dec de ; 6
ld a,d ; 4
or e ; 4
jp nz,loop ; 10
jp _performance_testGiven the Z80 running at 4MHz:
- loop takes 2.37 ms when reading from
$2000(a normal address in memory). - loop takes 2.50 ms when reading from
$d000(an address in video memory).
- ceda2vga: connect the motherboard of your huge Sanco to a small VGA monitor, to avoid it taking up all your desktop space.