Editing Commodore 64C

{{Infobox computer
| name         = Commodore 64C
| image        = [[File:C64c system.jpg|250px]]
| caption      = Commodore 64C in the low-profile “wedge” case (1986 revision)
| manufacturer = Commodore Business Machines (CBM)
| type         = Home computer
| release date = 1986&nbsp;(world-wide roll-out finished in 1987)
| discontinued = April&nbsp;1994
| price        = US$149 (1986 “Computer Only” pack)<br/>US$199 (1987 “Light Fantastic” bundle)
| cpu          = MOS 8500 (6510-compatible) @ 1.02&nbsp;MHz (NTSC) / 0.985&nbsp;MHz (PAL)
| memory       = 64&nbsp;KB RAM, 24&nbsp;KB ROM<br />(16&nbsp;KB combined Kernal + BASIC 3.0, 4&nbsp;KB character ROM, 4&nbsp;KB I/O)
| storage      = External cassette (1530 Datasette), 5.25″ floppy drive (1541-II), optional 3.5″ (1581)
| display      = 320 × 200 pixels, 40 × 25 text, 16 colours
| sound        = SID 8580 R5: 3 voices, 4 wave-forms, programmable filter, ADSR
| dimensions   = 40.6 cm × 21.6 cm × 5.7 cm
| weight       = 1.6 kg
| os           = Commodore BASIC 2.0 (in ROM)
| predecessor  = [[Commodore 64]]
| successor    = [[Commodore 128]] / ‘‘C64 GS’’ (console)
| codename     = C64C / “Aldi” (Aldi-specific cost-reduced board)
| model        = C64C, C64G, C64 Aldi, Educator 64C
| logo         = [[File:Commodore 64 logo-00.svg|250px]]
}}

The '''Commodore 64C''' (often shortened to '''C-64C''' or simply '''64C''') is the cost-reduced, slim-line redesign of the original [[Commodore 64|Commodore 64 “bread-bin”]].  Introduced during 1986, the C64C kept full software and peripheral compatibility while lowering manufacturing cost, power consumption and heat output.  Roughly four million units of the new style were produced, helping extend the C64 family’s commercial life to 12 years.

== Architecture and Processor ==
* '''CPU : MOS 8500''' — an HMOS-II shrink of the 6510, fabricated on 2 µm silicon and running from a single +5 V rail.  
* Clock rates remain '''≈1 MHz NTSC (1.023 MHz)''' and '''≈0.985 MHz PAL'''; timing is generated by the 8701 IC (short boards) or discrete VCO (early C64C boards).

Improvements over the original 6510  
* ~35 % lower power draw.  
* Input/Output port tolerant of 5 V logic only (no longer rated for 9–12 V).  
* Slightly faster rise/fall times on the address bus, easing DRAM timing margins.

== Memory and ROM Map ==
{| class="wikitable"
! Region !! Size !! Device !! Notes
|-
| $0000–$9FFF || 40 KB || DRAM || Main user RAM
|-
| $A000–$BFFF || 8 KB || BASIC 2.0 (within 16 KB ROM) || Bank-able
|-
| $C000–$CFFF || 4 KB || I/O or RAM || VIC-II, SID, CIAs, colour RAM
|-
| $D000–$DFFF || 4 KB || Character ROM / I/O || Bank-able by CHAREN
|-
| $E000–$FFFF || 8 KB || Kernal ROM (shared 16 KB chip) || Bank-able
|}

* '''DRAM''': two × 41464 (64 K × 4-bit) rather than eight × 4164; reduces board area and current draw.  
* '''ROM''': Kernal and BASIC are merged into a single 16 KB 23128 (or 23C64 mask) ROM, socketed at U4.  
* '''Character ROM''' (U3) unchanged (4 KB 2332 mask), but later boards use a 27C64 EPROM-compatible pin-out.

== Display and Graphics ==
Graphics are provided by a new HMOS VIC-II family:

{| class="wikitable"
! Variant !! Region !! Supply !! Note
|-
| 8562 || NTSC || +5 V only || Drop-in for 6567 R8 when crystal + jumper changed
|-
| 8565 || PAL B/G || +5 V only || Output phase compatible with PAL-B monitors
|}

Key specifications remain the same:

* '''320 × 200''' bit-mapped or 40 × 25 text.  
* '''16-colour''' palette (with HMOS slightly cleaner chroma).  
* '''8 hardware sprites''', sprite/multi-colour mode and line/column smooth scrolling.  
* Raster interrupts driven by the VIC-II still allow “raster bars”, split-screen scrolling and other demo effects made famous on the original C64.

== Sound – SID 8580 R5 ==
The 64C introduced the '''MOS 8580''' HMOS SID:

* Runs from '''+9 V''' (derived from the 9 VAC through a simple half-wave rectifier and 7809 regulator).  
* Significantly lower background noise than the NMOS 6581.  
* Filter curves were redesigned; many 1980s tunes written for the 6581 sound “tamer” on the 8580 unless software adjusts resonance values.  
* Paddle inputs now require 100 kΩ potentiometers (versus 470 kΩ on 6581).

== Input/Output and Expansion ==
All ports are retained:

* '''Cartridge / expansion port''' (for game carts, REU, RAMLink, etc.)  
* '''Serial IEC bus''' for 1541-II / 1581 drives and printers.  
* '''User port''' (RS-232, parallel adapters, BBS modems).  
* '''Two DB-9 joystick ports'''.  The C64C motherboard adds static-protection diodes on these lines.  
* '''Composite video + separated chroma/luma''' on the 8-pin A/V DIN (RF modulator still present for TV use).

== Cost-Reduction Motherboard Revisions ==
{| class="wikitable"
! Assy No. !! Nick-name !! Key changes !! Used chips !! Used in
|-
| '''250425''' || – || First C64C board; electronically identical to late bread-bin. 12 V SID (6581) still used. || PLA (906114-01), 8701 absent || Early 1986 transition units
|-
| '''250466''' || “Long 64C” || Added HMOS 8500 CPU & 856x VIC; still eight DRAMs. || PLA (906114-01) || Mid-1986
|-
| '''250469-(A/B/C)''' || “Short board” || Major integration:  
* New '''Super-PLA''' 251715-01 / 252535-01 (also contains colour RAM & 74LS257 logic).  
* DRAM reduced to two × 41464.  
* On-board 8701 clock generator. || Super-PLA; HMOS logic; 8580 SID || Late 1986–1994
|-
| '''250469-Aldi''' || “Aldi C64” || Ultra-low-cost run for Aldi supermarkets (Germany, 1993).  Uses 8500 CPU + 6581 SID (!) on a 5 V-only board; additional 7812 fitted. || Same as short board plus linear 12 V reg || 1993
|}

The Super-PLA runs ''cool'' and is considered highly reliable compared with the original ceramic PLA.

== Maintenance & Common Faults ==
* '''PSU failure''' – original “brick” still prone to over-voltage; modern protected PSUs (C64 Saver, new-build bricks) are strongly recommended.  
* '''Yellowed case''' – C64C plastics are ABS and will photo-degrade; [[Retrobrite|retrobright]] procedures restore colour but weaken plastic if over-done.  
* '''8580 SID shortages''' – originals are scarce; ARM-SID / SwinSID-Ultimate provide excellent substitutes and can emulate both 8580 & 6581.  
* '''RAM & colour-RAM''' rarely fail on the short board; the next most common faults are the 8701 and the RF modulator solder joints.

== Troubleshooting Highlights (Differences vs. Bread-bin)==
{| class="wikitable"
! Symptom !! C64C-specific suspect !! Notes
|-
| Black screen, no border || DRAM (U10/U11 41464) or Super-PLA || PLA failures rare but possible if it overheated
|-
| No sound || 8580 SID missing +9 V OR 7809 blown || 9 V derived from AC; check fuse F1
|-
| Keyboard dead || CIA U1 (8521) || Same matrix as original C64
|-
| Pink/green raster noise || 8701 clock chip || Swap with known good or install oscillator mod
|}

For fault-finding refer to the [[Commodore 64C Troubleshooting Guide]] (companion page).

== Technical Manuals ==
* ‘‘Commodore 64C/C64G Service Manual’’ (P/N 314001-03, 1992) – full schematics for 250425, 250469-A/B boards.  
* ‘‘Commodore Semiconductor Group Data Book’’ (1989) – electrical specs for 8500, 8562/8565, 8580, 251715.  
* ‘‘Commodore 64 Programmer’s Reference Guide’’ – unchanged from the bread-bin edition (all software compatible).

== Gallery ==
<gallery mode="packed" heights="180">
File:Commodore 64C - PD.jpg|Front view of a 64C
File:Commodore 64C - PD - tył.jpg|Rear ports (8-pin A/V, RF, IEC, cartridge, user, cassette & power)
File:Commodore C64C Mainboard.JPG|Assy 250469 Rev B “short” motherboard
File:SID chips.jpg|MOS 8580 R5 (HMOS) sound chip
</gallery>

== Related Pages ==
* [[Commodore 64 Troubleshooting Guide]] – applies to early C64C boards with 906114-01 PLA  
* [[Commodore 64C Troubleshooting Guide]] – short-board-specific diagnostics  
* [[Commodore 128]] – the 64C’s 1985 “big brother”  
* [[ARM-SID]] – modern SID replacement  
* [[Commodore 1541-II]] – cost-reduced floppy drive bundled with later 64C packs

[[Category:Commodore Systems]]