Pinout diagram
Used in Retro Machine Hubs
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Summary specifications
Full pin reference
| Pin | Name | Group | Direction | Levels | Description |
|---|---|---|---|---|---|
| 1 | NC | No Connect | Not connected | NC | No connection. |
| 2 | NC | No Connect | Not connected | NC | No connection. |
| 3 | ENABLE | Control | Input | TTL | Output Enable (tied to +5 V VCC in C64 and C128). |
| 4 | VSS1 (GND) | Ground | Power | 0 V | Oscillator ground (0 V). |
| 5 | NC | No Connect | Not connected | NC | No connection. |
| 6 | COLOR CLK | Clock / Timing | Output | TTL clock | Colour Clock output to VIC-II Pin 21 (17.734 MHz PAL / 14.318 MHz NTSC). |
| 7 | VCC1 (+5V) | Power | Power | +5 V | Output buffer +5 V supply. |
| 8 | DOT CLK | Clock / Timing | Output | TTL clock | Dot Clock output to VIC-II Pin 22 (7.882 MHz PAL / 8.182 MHz NTSC). If dead, the VIC-II cannot generate PHI0 for the CPU! |
| 9 | VCC2 (+5V) | Power | Power | +5 V | Core oscillator +5 V supply. |
| 10 | VSS2 (GND) | Ground | Power | 0 V | Core digital ground (0 V). |
| 11 | NC | No Connect | Not connected | NC | No connection. |
| 12 | NC | No Connect | Not connected | NC | No connection. |
| 13 | TON (PAL/NTSC) | Control | Input | TTL | Multiplier Ratio Select: Grounded (0 V) = PAL (x9/16); High (+5 V) = NTSC (x4/7)! |
| 14 | XTAL OUT | Clock / Timing | Output | Crystal | Crystal oscillator output. |
| 15 | XTAL IN | Clock / Timing | Input | Crystal | Crystal oscillator input (from 17.734 MHz PAL or 14.318 MHz NTSC crystal Y1). |
| 16 | NC | No Connect | Not connected | NC | No connection. |
Common uses and repair diagnostics
On early Commodore 64 boards (ASSY 326298 and 250407), Commodore used a complex discrete analog PLL circuit inside a silver tin box (built around a 74LS629 VCO and 74LS193 divider) to generate both the Color Clock and the Dot Clock for the VIC-II. Starting with the ASSY 250425 and 250466 C64 motherboards — and on every Commodore 128 and SX-64 — Commodore replaced that entire PLL circuit with a single 16-pin chip: the MOS 8701 (U31 on C64, U28 on C128)! Using internal delay lines and XOR frequency multiplication, the 8701 takes a single 17.734 MHz (PAL) or 14.318 MHz (NTSC) crystal and outputs both the doubled Color Clock (Pin 6) and the 8 MHz Dot Clock (Pin 8) into the VIC-II.
Used at U31 in Commodore 64 boards (ASSY 250425 and 250466), on the SX-64 PLL sub-board, and at U28 in the Commodore 128 and C128D. Note that the exact same MOS 8701 part is used in both PAL and NTSC machines — jumper J2/J3 simply grounds or lifts Pin 13 (TON)!
- On a Black Screen C64 (ASSY 250425/250466) or C128: if VIC-II Pin 17 (PHI0) has no 1 MHz clock, immediately scope Pin 6 (COLOR CLK) and Pin 8 (DOT CLK) on the 16-pin 8701! A dead 8701 leaves the entire system clockless.
- Black-and-white picture or shimmering rainbow snow on composite/S-Video: lightly clean the 16-pin 8701 socket and adjust the small ceramic trimmer capacitor (CT1) next to the crystal.