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C > COMMODORE  > C128 - C128D


Commodore
C128 - C128D

Untitled Document

Taneli Lukka's point of view:
The C=128 is really just an expensive C=64, atleast for the normal hobby user. The C=128-mode has a pretty powerful basic and other new features, but the most important selling factor: games, never appeared because developers were afraid that they might lose the huge C=64 user base by concentrating on the C=128 and as a result only very few games were made together with some "serious" programs. Some disk based C=64 games do take advantage of the C=128 by having an auto boot feature, like most Amiga games, but there are very few games like that, Project Stealth Fighter from Micro Prose is one.

The CP/M mode is pretty useless too because it is quite slow. The Z80 has to be slowed down so that the I/O circuits can keep up with it. Really great engineering from Commodore.

For todays user the main problem is the power supply which was only used with the C=128 and as a result finding a new one if the original stops working or gets lost is very difficult indeed.

Music makers also dislike this model like the C=64c because the SID-chip sounds diffirent than the original.

Shaun reports to us:
I was reading you information about the Commodore 128 with great interest. It's nice to know that you got so many things correct. You did however leave out the expandable bit. Both the 128 and 128d can be internally expanded to 1,024kb, as the 8502 chip can handle 16 banks of 64k. All 16k vdc ram can be upgraded to 64k - this allows you to handle hi-res colour interlacing (640x400) and colour mixing upto 4096 colours (the same resolution and colour amount as the older Amigas).

Also, all models of the Commodore 64/64c and 128/128d can, thanks to an American company, be extrenally upgraded to 16mb. (Commodore, themselves, used to make ram expansions for the C64/128 upto 512k, which could be made upto 2mb.)

In 1995, a company called Creative Micro Designs, decided to develop an accelerator card which would allow use of standard 72-pin simms ram upto 16mb. After much development, they where sucessful - the 128 version of this upgrade was not for another year or so, but now you can buy accelerator cards/ramcards for your C64 and 128 - in theory, as this accelerator is compatible with the old Commodore ram expansions, the maximum memory for the C64 is 34mb and for the 128 is 35mb (remember - C128 allows1mb internal also!)

CMD (Creative Micro Designs) made a lot of C64 hardware between 1986-1997, and where still selling these upgrades in 2000/2001 - the Commodore part of the operation was then sold to Click Here Software, who still continue CMD's legacy.

If you can imagine for a minute, I have sitting in my spare room the following system - set and and fully working;

Commodore 128 - 16bit 65c816s processor at 20mhz and 16mb's simms (SCPU Accelerator and SuperRAM card) - 16mb Ram disk (upto approximately 256k per second loading - a lot faster than 50k per 5 seconds on the old 1541!!) - inteligent 3 button mouse with y2k compatible real time clock - 3.5" disk drive formatting upto 1.6mb per disk and fast data transfers - Printer interface running Canon BJC 4100 - 1571 and other authentic Commodore drives.

Now, you may ask yourself, how compatible is all of this stuff? Well, each device may be switched out, and the accelerator can be switched down to 1/2mhz, so for backwards compatibility, it's 100% in a roundabout sort of way - or in other words I don't have to plug/unplug all the upgrades depending on what I want to do.

Ron Shirley adds:
I have just been looking through your website and i must admit i am very impressed. However in the commodore c128d information, Imust question part of the report from "shaun" where he says that the 64k vdc upgrade for the c128d enables 4096 colour mixing.

To the best of my knowledge all the 64/128 video output is limited to 4bit (only the lowest 4 bits are connected, the upper 4 bits don't do anything) this gives a limitation of only 16 colours. The 16/64k vdc is only used in cpm mode using the "RGBI" output socket in 40 column mode you can use the 64k vdc as a data cache when copying disks, many copiers such as "maverick" made use of the 64k vdc if available (the vic ii chip is used in 40 column mode not the vdc so its memory can be used).

As for upgrading the memory internally to 1MByte, all the memory chips in the 128 are soldered in place and there are no available sockets to support such an
upgrade internally. It's true that the c128 supports memory banking but it's not to support 1 MByte of internal memory but to support the 2x 64k banks in various configurations due to the limitations of the 8bit processor it can only access 64k at a time. It therefore has to have enough memory bank options to support both 64k
banks and each bank with or without basic or kernal roms e.t.c.

bank 0 ram(0) only
1 ram(1) only
2 ram(2) only (same as 0)
3 ram(3) only (same as 1)
4 internal rom,ram(0),I/O
5 internal rom,ram(1),I/O
6 internal rom,ram(2),I/O (same as 4)
7 internal rom,ram(3),I/O (same as 5)
8 external rom,ram(0),I/O
9 external rom,ram(1),I/O
10 external rom,ram(2),I/O (same as 8)
11 external rom,ram(3),I/O (same as 9)
12 kernal and internal rom (low), ram(0),I/O
13 kernal and external rom (low),ram(0),I/O
14 kernal and basic rom, ram(0), character rom
15 kernal and basic rom, ram(0),I/O

Some items missed out:
The c128 can run in either 1 or 2 Mhz mode but none of the other chips in the c64 mode can support 2 Mhz so the screen is switched off and the ports are disabled. It can be accessed by :
LDA #$00 = 1 mhz
LDA #$01 = 2 mhz
STA $d030
This caused compatability problems with some tape loaders they were overwriting the area $d000 and up (sprite pointers) causing the machine to crash.

Another bit of trivia:
The tape version of the game "yie ar kung fu" does not work on the 128D , this is because of copy protection which forces you to switch off your disk drive during tape loading. a bit dificult (but not impossible) on the 128D.

And another.
Possible damage can be done to the buffer device controlling the keyboard and joystick ports on the c128. The c64/128 uses shared locations between joystick port-0 and some of the keyboard. When an autofire joystick is used for an extended period of time it can damage the locations in the buffer device causing a strange effect. When you unplug the joystick and switch on the c128 everything appears normal until port-0 is read by a program or game, the locations inside the buffer device then latch causing several keys on the keyboard to stop responding until the power is switched off and then on. I have noticed 4 or 5 machines with exactly the same cause and effect.

Best hardware upgrade.
The phantom parallel board for the cbm1541 diskdrive it took loading times from 0sec-2mins without the board to 0sec-4sec with the board (incredible!). Both sets of times are without software turboloaders.

More information about the Z80 and VDC chips, by Michael Huth:
The Z80 runs in a weird timing to be compatible to the VIC II. The VIC II uses 16 KB of the main ram and the VDC can use upto 64KB seperated ram. The C128 was delivered with 16KB seperated ram for the VDC. The speed of the 8500 in C128 mode is at 1 MHz exactly the same as in C64 Mode. In 2 MHz mode its a little faster than 2x because of the VIC II badline cycles missing. The VDC itself is clocked completely independent and asynchroneus. (about 2MHz and VDC RAM at 16 MHz)





 
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