Apple //c
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(pictures copyright by M.A.Grundke)
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The Apple //c
Apple Computer, Inc.
Cupertino, California | 2A2S4-050948 (=serial number) |
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Apple //c opened up overview:
quite narrow in there; main reason for that is the machine's integrated 5.25 inch diskdrive (right side). Since 3.5" disks were uncommon and expensive these days, and lots of Apple ][ software was already available on 5.25" disks, Apple decided to integrate the drive - together with the carrying handle (back of the machine) and the compact design, you had quite a portable machine. The power supply, however, was still external - what you see on the machine's
left is just a power converter for the external PSU. The keyboard is quite a good one and comfortable to use (at least for me). On the SPACE key, by the way, there's still the original DEUTSCH (i.e. german) sticker, implying this keyboard has a german layout. Interesting: in 1988, Apple released the Apple //c Plus with integrated 3.5" drive and integrated power supply |
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MAIN LOGIC 820-0115-C overview:
this is the earliest, so-called 'Original //c' board. It uses the original ROM revision, which was unable to control UniDisk-drives. Furthermore, it lacked some serial I/O functions and had no memory expansion slot (which came with the 1986 so-called 'Memory Expandable //c'). Now let's have a look at the components,
from left to right: you can easily spot the large internal power converter (which is needed in addition to the external 18W power supply). Below it, volume knob and headphones jack. To the right, below the blue keyboard-connector are the //c's keyboard controller, and again right from there, the keyboard- (at C22) and monitor-ROMs (C2, below). Further right are three chips, IOU (topmost at C4), MMU (C3) and CPU (C1). To their right is the memory bank (consisting of 16 pcs. 64Kx1), which extends from the
machine's front to its back. Now moving up from the blue keyboard connector, you come across the two 6551 ACIAs (C33), and above them (in that order) GLU (C15), TMG (C13) and IWM (C24). Right from these are the character generator (C25) and the 80 latch logic below it, left from there the small MC1488PD and MC1489PD (serial line driver and receiver) |
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board silkscreening, part 1 (left pic):
MAIN LOGIC
820-0115-C
APPLE COMPUTER
(C) 1983
Beneath it, the board's internal 'POWER SUPPLY' connector (J11). Despite of its name, the device plugged here (see right pic) is just a power converter for the external power supply |
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board silkscreening, part 2:
D612-0128-A |
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board silkscreening, part 3:
(C) MICROSOFT 77
(C) APPLE 1977 - 1983
Before it, you can see the machine's internal speaker |
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board silkscreening, part 4:
apple® computer ©1983 |
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| The Apple //c comes with a NCR 65C02A as CPU, an enhanced MOS 6502 running at 1.02 MHz and designed by Western Design Center, Inc. (WDC). Enhancements include CMOS production process (less power consumption) and 27 additional intructions (although hardly used because of Apple ][ compatibility). Note that the later Apple //c Plus came with a 4 MHz CPU of the same type and some changes in design related to it (like SRAM cache).
The 65C02, however, also found its way in the Apple //e enhanced (March 1985) and Apple //e Platinum (January 1987, a //e enhanced with a different case and numeric keypad) |
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| As the name implies the MMU (Apple partno. 344-001) is used for memory management, i.e. mainly memory bank switching (since the 65C02, like its 6502 ancestor, has a 16 bit address bus and thus can only access 64 KBytes directly). Additionally, MMU redirects I/O access operations to the IOU where the afflicted addresses are decoded. By the way, CPU/ MMU and video logic have to share memory bandwith. The MMU accesses RAM in one cycle, the IOU in the next |
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| The Apple //c's RAM bank, consisting of 16 pcs. Mitsubishi M5K4164ANP (64Kx1 DRAM). These 128 KBytes were by far enough for most Apple ][ applications; anyway, later board revisions (the so-called 'Memory-expandable //c') had a memory expansion slot allowing expansion to 1 MByte. According to some sources, the Apple ][ design should be able to take up to 8 MBytes RAM (which would require lots of bankswitching, of course) |
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| The Apple //c's ROMs, 341-0151-A (keyboard ROM Rev.A german/US, also used in the european //e) and 342-0272-A (monitor ROM). The keyboard ROM provides the machine's ability to switch between to layouts (german QWERTZ and US QWERTY in this case). Of course the character generator must be able to create the appropriate characters. The monitor ROM, however, contains machine language monitor, Applesoft BASIC, assembler/ disassembler and the 80 latch firmware.
This 342-0272-A , by the way, is the 'original //c ROM', which was unable to control UniDisk-drives. But it can easily be upgraded to the '3.5 //c ROM', which can. To find out the machine/ROM revisions just enter BASIC-mode and type PRINT PEEK (64447). A decimal number from memory location $FBBF will appear, telling you which //c-revision you have: |
| $FBBF value HEX | $FBBF value DEC | Apple Part No. [1] | Machine/ ROM revision |
| $FF | 255 | 342-0272-A | Original //c without Unidisk capability. Serial: no XON/XOFF or masking of incoming LF-characters |
| $00 | 0 | 342-0033-A | 3.5 ROM //c with Unidisk capability. Serial: has XON/XOFF and masks incoming LF-characters by default |
| $03 | 3 | 342-0445-A | Original Memory Expandable //c ('memx') with Unidisk capability. Can use //c memory expansion card. Serial: same as '3.5 ROM //c' |
| $04 | 4 | 341-0445-B | Revised Memory Expandable //c with Unidisk and //c memory expansion capability. Same as 'Original Memory Expandable //c', but with firmware fixes |
| $05 | 5 | 341-0625-A | Apple //c Plus. Supports Unidisk and Apple 3.5" formats. Cannot use //c memory expansion card anymore. //c Plus features include integrated UniDisk drive, 4MHz 65C02, internal power supply and Apple standard keyboard |
[1] As far as the part numbers are concerned, note that more different numbers may exist for the same ROM revisions. So should you know other part numbers, you're welcome to contribute them
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| The Apple //c's keyboard encoder, the General Instruments (GI) AY-5-3600-PRO. Although it was very popular and should still be widely available today, it is, in case of defect, often replaced by the SMC KR3600 or KR9600 (the KR3600 is functionally identical to the GI AY-5-3600-PRO, the KR9600 is its successor) |
| David Wilson from University of Wollongong, Australia, adds the following information (thanks, David!): |
| This version (-PRO) does not generate ASCII - it just reports a number from 0-127 indicating which key was pressed. The keyboard ROM maps this number (with control + shift and capslock modifiers) into the ASCII code. |
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| The 'Input/ Output Unit' (IOU, Apple partno. 344-0023-A). Its main purpose is video display creation and output, but it's also used for address decoding and I/O access operations in general, and works hand in hand with the MMU. When introduced with Apple //e and //c, both IOU and MMU replaced lots of TTL ICs used in the older Apple ][s. That didn't only reduce production cost but also improved reliability |
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| The german //c character generator, Apple partno. 342-0275-A. It outputs US- or german characters, depending on which keyboard-layout is selected by keyboard-ROM/ keyboard layout switch. The Apple //c's character generator was the first in the Apple ][ series to include pictorial characters (so-called 'MouseText', adding 32 new characters by replacing flashing characters in 80 column mode), which could be used for creating graphics or nicer pulldown-menus. The new character generator ROMs were also available for the Apple //e as 'Apple(TM) //e enhancement kit'
(together with 65C02 CPU and new monitor ROM), making it an Apple //e enhanced, effectively |
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| 341-0243-A GLU ('General Logic Unit') and, behind it, 341-0170-A TMG ('Timing Generator'). GLU provides basic logical functions mainly for the machine's I/O subsystem, whereas TMG generates timing signals for data- and address-buses, for video refresh etc. Exact information on GLU and its functions is, however, quite rare. Should you have any, please contact me! |
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| A closer view on the Apple //c's audio section. Audio is created and controlled by 343-1002 'AUD' (top of the picture); it controls both the internal speaker and speaker volume, and outputs sound to the headphones jack ('AUX SPKR'). Since sound is created by just turning the speaker on and off (and doing it very fast to create tones), it's good the Apple //c's got a volume knob ('VOLUME CONTROL')... However, with 'tricks' it was even possible to play digitized soundsamples, although in poor quality. Worth a note is that there were 3rd-party expansions, early soundcards,
which greatly improved the Apple ][-series sound capabilities (like the famous 'MockingBoard', which added a General Instruments AY-3-8192 to the machine). Although most of these were expansion cards and thus not usable with the //c, some could be connected via serial |
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| 344-0041-A 'IWM' is the diskette controller for the integrated 5.25 inch drive. Left behind it, part of the internal floppy connector (blue) as well as video output - you can see part of the composite jack and SUB-D RGB-port, with 'VID' (343-1001) before them. According to the schematics, VID takes up signals from SPI, TMG and IOU to create the actual video output. However, exact details are hard to get - anyone out there with more info? Interesting to know is also that early Apple ][ didn't come with a diskette controller, it had to be added as expansion card. Instead, cassette recorders could be
attached using 'cassette I/O' (i.e. two audio connectors for in- and output). Cassette I/O was integrated in Apple ][, Apple ][+ and Apple //e, and dropped upon introduction of the //c. As far as disk operation is concerned, furthermore, it's notable that the Apple ][+ was the first to add automatic startup from disk (new monitor ROM revision) |
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| In earlier Apple ][s you had to buy the 80-column extension seperately, as expansion card. In the Apple //c (and the //e-series), it came integrated onboard (80 LATCH/ 80 DIR) - nice. This section of the board (consisting of SPI, 80 LATCH, VIDEO LATCH and 80 DIR - all TTL ICs) is essential for creating the video output - together with the character generator and VID (shown below, above IWM), and incorporating signals from TMG and IOU |
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| Motorola's MC1488 (quad-line driver) and MC1489 (quad-line receiver) are very common parts, used for RS232-compliant serial communication in many 1980s and 1990s computer designs. They provide the machine with RS232 hardware-level communication (i.e. producing the correct signal levels), and are, in the Apple //c, controlled by the two R6551 ACIAs (see below) |
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| These two Rockwell R6551 ACIAs are used for serial I/O - in fact, they provide the high-level functions, while MC1488/ MC1489 (mentioned earlier) are responsible for creating the appropriate signal levels (i.e. low-level communication). In this earliest //c-design, the serial firmware doesn't support the XON/XOFF flow control, which caused problems with some serial devices such as fast modems |
| Again, here's some info provided by David Wilson, Australia, this time about serial communications: |
| The problem is actually worse. The original //c design cheated and did not use a 1.8432 MHz xtal.
Instead it used a 74S161 at location UC7 to divide the 14.31818 MHz oscillator frequency by 8 giving 1.79 MHz which was close enough for 300bps modems but not good enough for 2400bps and above. My original //c has a modification replacing UC7 with a 4 pin oscillator with some extra wiring. |
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| The Apple //c from behind. Here you can see how the carrying handle was probably used most times: to alter the keyboard angle. Connectors from left to right: joystick/ paddle SUB-D (yes, only one port!), DIN serial port #2, RGB out SUB-D, composite video, external diskdrive SUB-D, DIN serial port #1, PSU connector and finally, the power switch.
Note that the RGB out requires an additional adaptor to connect to a monitor, but it can be used to directly connect the rare Apple LCD (a small b&w LCD screen which fits onto the machine). As for the serial ports, the DIN connectors used here were replaced with mini-DIN connectors in the Apple //c Plus design |