Commodore Plus/4
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(pictures copyright by M.A.Grundke)
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serial number: DA4 65426
'DA4' was a german Commodore production facility. |
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Overview of the ASSY 310163 board:
it's higher integrated than the C16's, since it holds more RAM, more ROMs and the user port with its additional logic. Now from left to right. Compared to the C16's board, both Plus/4 and C116 have their RF-modulator on the left side. The internal keyboard connector's just a cheap flat-foil cable, but not as cheap like the ones used in early Sinclairs (which were easily broken).
Advancing further to the right, there's the expansion connector (e.g. for a CBM 1551 or cartridges) and below it, TED (U1) in its shielding. Yes, it's shielded and passively cooled with a copper tongue. Interesting to know is that the C16 only has a cheap cardboard-shielding, and in the C116, the complete board is shielded (not just TED alone). Below TED, however, is one of the two MOS 6529B (U27, left from the keyboard connector, with three 74xx), and heading right again, the Plus/4's ROM bank (TED KERNAL at U23, TED BASIC at U24 and the two function ROMs at U25 (LOW),U26 (HIGH) containing the 3-plus-1 software).
Then, next to the function ROM HIGH follows the PLA (U19), and the RAM bank (8 pcs. 64Kx1, U11-U18). Then, above PLA and RAMs, resides the CPU (U2) and right from it, the ACIA (U3). Between CPU/ ACIA and the user port on the board's back (just right from the cartridge interface), finally, is the second MOS 6529B (U5) between two 74xx (logic circuits) at U4 and U6. An interesting fact that all members of the 264-series have a completely different board - normally you would except Commodore to use the same board with different configurations for cost-reduction. The exact reason is unknown; the Plus/4's board, however, is identical to the C264 prototypes's (the C232, again, uses a different board) |
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board silkscreening:
ASSY NO. 310163 |
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board silkscreening, part 2:
W-18 94HB |
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| The Plus/4's CPU is the MOS 8501 (location U2), which is fully software-compatible to its ancestor, the MOS 6502, used in earlier Commodore computers, but comes with an additional 7 bit I/O port (which was especially added for the 264-series' board design - it's connected to TED, PLA and expansion connector). It was manufactured in Commodore's HMOS-2 process (a high-speed version of the older NMOS-process). Some machines came with a MOS 7501, which is the HMOS-1 equivalent;
interesting is that even the earliest machines I found here in Germany had a 8501 (even my C232), which implies that the HMOS-1 chips where either produced in small quantities or that most of them were used for production outside of Europe (like the US). However, exact details are unknown (yet) |
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| The Plus/4's RAM bank, 64 KByte implemented as 8 pcs. 64Kx1-organized chips (Samsung KM4164A-15 in this particular machine, locations U11-U18). When taking a look back on the 264-series, you might wonder that there were two 16K-machines (C16 and C116), and then a large gap to the Plus/4 with its 64 KBytes. Well, this gap would've been closed if the C232 had made it to the market. This 32K-prototype was intended to become the entry-level machine of the series, which was originally conceived as a professional addition to the
exisiting 64-series - with two 64K machines (C264 and CV364). But both C232 and CV364 (which was a C264 with Magic Voice cartridge integrated onboard) remained prototypes, and the C264 was renamed to Plus/4. The whole series was a complete failure and due to a change in Commodore's management these days, already abandoned when they were launched (a shame, since the TED architecture is quite interesting) |
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| This is TED (MOS 8360, here in revision 2, at U1), which makes the 264-series so special. Although TED is short for 'text editing device', it integrates nice 128 color graphics and three voice sound in one piece. That does reduce production cost, but there are major drawbacks to that 'all-in-one' solution: first of all, it was just incompatible with the popular C64; second, TED's capabilities cannot rival the C64's VIC-II/ SID combination - TED is missing Sprites, for example, making it unsuitable for games, and although it can output three voices, it only integrates two sound generators
with limited capabilites (SID's got four independant voices and much more possible sound effects). After all, the 264-series wasn't conceived for gaming but for serious work. Also interesting is TED's shielding - in comparison with C16 (with primitive cardboard shieling for the whole board) and C116 (with better board-shielding and a cooling tongue for TED), Plus/4's TED has its own shielding and a copper-tongue for cooling - see below. Note that TED shown here was produced in 1986 (all other parts are from 1984), which either means it was replaced in 1986 or later, or the complete machine was sold in 1986 (probably in a sell-out at the german Aldi-Disount or Vobis chain) |
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| The above-mentioned upper part of TED's shielding, with the copper cooling tongue attached. For better contact with the chip, you can see cooling paste on it. Again, only Plus/4 and C116 have shielding and cooling tongue for spreading the heat (although in the latter, shielding covers the whole board and the tongue is not copper). In the C16, TED isn't cooled at all - but nevertheless works (maybe not necessary because of the larger case?) |
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The Plus/4's ROMs, part 1:
C318004-05 ('TED KERNAL', revision 5, U24) and C318006-01 ('TED BASIC', revision 1 - do other revisions exist?, U23). KERNAL contains the character set and a useful machine language monitor ('TEDMON'), which can be invoked with the MONITOR command in BASIC. These ROMs can be found in all 264-series machines, although KERNAL exists in different revisions and for different TV standards (PAL-G or NTSC-M, maybe more) |
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The Plus/4's ROMs, part 2:
C317053-01 ('FUNCTION ROM 3+1 LOW', U25) and C317054-01 ('FUNCTION ROM 3+1 HIGH', U26) occupy the Plus/4's function ROM sockets and contain Tri Micro's 3-plus-1 software collection. It contains four simple applications: text-processor, spreadsheet, graph-tool (integrated in spreadsheet) and a file-manager (some even call it a simple database). The concept of using function ROMs was very promising, since you could easily add new functions (like software) to your machine. These sockets can be found in Commodore computers from early PETs to
the 128-series. An interesting fact: when the 264-series was conceived as series of business computers, the C264 and CV364 were planned in different versions, each coming with different software in ROM (by the time those were 3-plus-1, Superscript, Logo or Magic Desk). However, Commodore dealers complained about these plans even before the first machines were shipped - they simply couldn't imagine how to store all those different versions, and how to determine which variants in which quantities should be put in stock. Before this became a logistical problem, Commodore management had already abandonded the inital plans; the C232 and CV364 were cancelled and the C264 became the Plus/4,
with Tri Micro's 3-plus-1 integrated in all machines |
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| Both C16 and C116 have only one 'Single Port Interface' (MOS 6529B), whereas the Plus/4 has two of them. A single-port interface contains, as the name implies, just one 8 bit I/O-port (i.e. 8 lines). As already mentioned, all 264-series contain at least one MOS 6529, which is responsible for keyboard I/O,
and partly for RAM and expansion port. In the Plus/4, the second 6529B is required to control the user port (together with ACIA and PLA, as described below). However, the left picture is from above the CPU (U5), the right from left of the keyboard connector (U27) |
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| The MOS 251641-02 is the machine's programmable logic array (in short: PLA, at U19). Like other Commodore computers' PLAs, MOS 251641-02 is a gate-array providing logic equations; the function of the PLA's gates heavily depends on the mainboard configuration and layout, thus PLAs are not exchangeable between different series. With its gates, the PLA provides adress selection and decoding for RAM, ROM and I/O, including the expansion connector (with any ROM or RAM connected to it, e.g. program cartridges or memory expansions) |
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| The MOS 8551 (U3) is a HMOS-2-produced version of the Synertek 6551, which was used in earlier Plus/4s (although I've never seen a HMOS-1 MOS 7551 - was it ever produced?). However, its purpose is serial, RS232-compliant userport communication, although the Plus/4's design is missing serial line driver and receiver chips - they had to be included in the expansion device itself (e.g. the modem), or added with an adaptor |
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| The Plus/4's back with most of its ports (only the RF-port is on the machine's left side). From left to right: square-type power supply connector (for PSU 310200-09), standard CBM IEC serial bus (e.g. for CBM 1541), mini-DIN CBM264 cassetteport (for CBM 1531), userport (which can be used for modems, centronics interface etc.; note that C16 and C116 don't have one!), the cartridge interface ('memory expansion', also used to connect
the parallel CBM 1551), the two mini-DIN joystick ports (for CBM T-1341) and, finally, CBM's 8 pin audio/video port. Interesting is that some (early?) machines had a round DIN powersocket, which allowed you to use standard C64 powersupplies |
Also see the other 264s, Commodore 16 and Commodore 116 !