Commodore 128D User Manual download pdf (Page 11)

Since I had ﬁnished the daughter board, I bent up the pins 2 and 5 of the U14 multiplexer chip, and connected its

pins 1–3 and 5 to the daughter board with wires. First I inserted the wires for A14 and A15 directly to the chip socket,

but as it turned out to be unreliable, I located a through-put place for each line, and soldered the wires there instead.

When you have wired the multiplexer U14, remove the jumper wire between MA8 and +5 V and connect that

address line to the daughter board. Then connect the PIA’s CS line to I/O2, which is in U3’s pin 7 (or one of the

through-put places along the trace’s path to the cartridge port), and insert the daughter board to the socket. Switch the

power on and pray that your dear computer works.

If you get only crap consisting of @’s or some randomly changing graphics on the 40 column screen, check that

all CIA pins have a good contact to the piggy-back socket, and that the wires from U14 and its socket are ﬁrmly

connected. If it doesn’t help, you have to check all daughter board connections with the continuity tester. Don’t panic,

you can ensure that the computer works by connecting the MA8 line back to +5 V, by bending the U14 lines back

down, and by inserting a spare CIA chip to the CIA socket.

2.3.4 Testing

After you have installed the boards to your machine, it is time to test the connections. You can connect LED, keyboard

and probably disk drive in addition to the power cable and the TV cable, but do not fasten the mounting screws yet. If

the 40 column screen shows up and if the machine seems to operate, input the following test program:

10 PB=57282

20 POKE PB,255:POKE PB+1,4:POKE PB,255

30 PRINT"PRESS A KEY AFTER THIS HAS DISAPPEARED":

FOR I=0 TO 3000:NEXT

40 POKE PB,14:WAIT 198,15:GET A$:POKE PB,255

On the line 10 a variable PB is set up. It is the address of the peripheral and data direction registers for the 6821

port B, and the block selection register of the segments 2 and 3 and the VIC-IIe.

The line 20 contains initialization of PIA: the lines PB0–PB7 are set outputs, the data direction register is switched

to data register with ‘POKE PB+1,4’, and the PB lines are set high.

On the line 40 VIC-IIe is given block 0 ($00000–$0FFFF) of the default bank (0), and then the program waits for

a keypress and restores the block F ($30000–$3FFFF).

If this test program works as expected, the screen will be ﬁlled with ‘@’s and other random characters.

At this point, you may want to switch to the C64 mode and to run the TEST program, which is among the distribu-

tion ﬁles.

Also, you can try the PIAGLOBE.128 program to test almost all of the 512 kB or 1024 kB memory.

The PIAGLOBE.128 program is based on Georg Schwarz’s globe spinner GLOBE.64 that uses two graphics screens.

He has made a slightly faster version for the C128, utilizing the 2 MHz mode in the screen border. But compared to it,

PIAGLOBE.128 is from other planet. Depending on the amount of memory available, it calculates 112 or 56 pictures

of the globe and then uses them in a continuous animation. One revolution will last approximately 2.23 seconds on

PAL systems and 1.87 seconds on NTSC. As the calculation phase lasts more than a minute, the program changes the

screen color between each picture.

On NTSC systems, the edge of the globe might not display correctly. The edge is rounded with 24 sprites, which

are moved around by a raster interrupt routine, starting from $4801. I did not bother to think about the timings, since

I had enough troubles with relocating the program and the tables, and in trying to get all that graphics data to ﬁt in the

memory. In the distant future I might make a better looking version of the globe spinner, who knows. There is over 80

kilobytes of unused memory when running the program on a C1028.

2.4 Expanding to 256 or 1024 kilobytes

This MMU expansion is far easier to understand than the PIA expansion, and maybe faster to build, too. You have to

solder the new MMU and a couple of logic chips on top of some chips laying on the mother board, or to install them

on a daughter board. I chose the piggy-backing method.

The biggest problem with this expansion is that the MOS 8722 MMU is a custom chip from Commodore, and

it is only used in the Commodore 128, which has not been manufactured for ages. If you do not happen to have a

See Section 5.1.

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Commodore 128D User Manual Page 11

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