I heard somewhere that the RGB output on Commodore 128s is not quite the same as the one found on PCs, and that 5153 monitors don't work with C128s, and 1902s don't work on CGA cards. It seems to be related to the scan frequency. Can anyone confirm this?
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CGA monitors
- Thread starter Fallo
- Start date
Zeela
Experienced Member
Hmmm... I have an old CGA-monitor (don't remember brand and model right now) and I use it for the 80-col output on my C128. Works like a charm.
The C128 has a non CGA-standard output as one of the pins of the C128's 9 pin DSub is monochrome composite video. I don't think you'll find that on a PC with a CGA-card.
The C128 has a non CGA-standard output as one of the pins of the C128's 9 pin DSub is monochrome composite video. I don't think you'll find that on a PC with a CGA-card.
Hmmm... I have an old CGA-monitor (don't remember brand and model right now) and I use it for the 80-col output on my C128. Works like a charm.
I don't know how well some CGA monitors work, I just heard that the 5153 is incompatible with the C128 and the 1902 incompatible with CGA. Supposedly you get a rolling picture.
BTW, if you're using a CGA monitor intended for a PC on the C128, you should get brown, correct? The 1902 obviously doesn't have the circuitry to change dark yellow into brown.
The C128 has a non CGA-standard output as one of the pins of the C128's 9 pin DSub is monochrome composite video. I don't think you'll find that on a PC with a CGA-card.
Pin 7 is used for the composite output. On CGA monitors, that normally isn't connected to anything. The scan frequency probably is a little different on the C128. Some monitors may be able to handle it better than others.
Heck, I've heard that 5153s don't like the 225-line text on Tandy 1000s, either.
Great Hierophant
Veteran Member
I don't know how well some CGA monitors work, I just heard that the 5153 is incompatible with the C128 and the 1902 incompatible with CGA. Supposedly you get a rolling picture.
BTW, if you're using a CGA monitor intended for a PC on the C128, you should get brown, correct? The 1902 obviously doesn't have the circuitry to change dark yellow into brown.
Pin 7 is used for the composite output. On CGA monitors, that normally isn't connected to anything. The scan frequency probably is a little different on the C128. Some monitors may be able to handle it better than others.
Heck, I've heard that 5153s don't like the 225-line text on Tandy 1000s, either.
I think in cases where uses reported incompatibility, the C128s were PAL machines, which output 50Hz. CGA and NTSC displays require 60Hz. Using a system designed for one scan rate on a monitor requiring a different scan rate will give you rolling.
As I read the C128's color choices, all the CGA colors, including brown, are present. Commodore does not use IBM's color names, but the palette is the same for the C128.
The 5153 does not have a problem with 225-line text, all you need to do is adjust the vertical size.
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I think in cases where uses reported incompatibility, the C128s were PAL machines, which output 50Hz. CGA and NTSC displays require 60Hz. Using a system designed for one scan rate on a monitor requiring a different scan rate will give you rolling.
Now that I think about it, that makes perfect sense, because since the VDC chip in the C128 has composite output, it would have to scan at 50Hz to be compatible with PAL displays. And thus PAL-region 1902 monitors also scan at 50Hz and are incompatible with CGA.
As I read the C128's color choices, all the CGA colors, including brown, are present. Commodore does not use IBM's color names, but the palette is the same for the C128.
The C128 has 4-bit RGB just like CGA. It follows that 4-bit RGB should always produce the same 16 colors, which includes dark yellow. According to this site, the C128 does indeed produce that color and not brown:
http://john.seikdel.net/vdcmadeeasy01.htm
It also says that most monitors will produce brown, however I assume that only ones designed for PCs do that (ie. clones of the 5153). Monitors such as the NEC Color Character Display and the Commodore 1902 that were intended for non-PC machines should display yellow.
The 5153 does not have a problem with 225-line text, all you need to do is adjust the vertical size.
That would be the maximum scan line register, correct?
Great Hierophant
Veteran Member
Now that I think about it, that makes perfect sense, because since the VDC chip in the C128 has composite output, it would have to scan at 50Hz to be compatible with PAL displays. And thus PAL-region 1902 monitors also scan at 50Hz and are incompatible with CGA.
The C128 has 4-bit RGB just like CGA. It follows that 4-bit RGB should always produce the same 16 colors, which includes dark yellow. According to this site, the C128 does indeed produce that color and not brown:
http://john.seikdel.net/vdcmadeeasy01.htm
It also says that most monitors will produce brown, however I assume that only ones designed for PCs do that (ie. clones of the 5153). Monitors such as the NEC Color Character Display and the Commodore 1902 that were intended for non-PC machines should display yellow.
That would be the maximum scan line register, correct?
No need to get that technical, the 5153 has a vertical size knob in the back of the machine, poking out the casing. Just fiddle with that a bit. There is also a vertical hold knob, which may cure your rolling problems.
Alternatively, you can use the Tandy DOS mode 200 command to give you back your 200 lines display.
I have a Magnavox that was used with a C128 and I had to adjust it when using it on a CGA PC to keep it from rolling using the built in knobs (nice monitor for the age).
Those Magnavox monitors were clones of the 1902 and were mainly intended for the C128. I would imagine they display yellow and not brown.
I have some success to report on this matter; I got a Tandy CM-11 on Ebay last week (after losing an auction for a 5153), but it hasn't arrived yet.
I have a Commodore 1084S-P1. It's a PAL-monitor but it also supports 60Hz (it does not support NTSC colors so composite CGA will appear black and white). As you can see, brown will be displayed correctly when it is used as a digital RGBI-monitor with CGA.
I don't have a C128 but 1084S manual says that C128 can be connected the same way as CGA (C128 can also be connected with S-video). Maybe 1902 also works as the same way?
I don't have a C128 but 1084S manual says that C128 can be connected the same way as CGA (C128 can also be connected with S-video). Maybe 1902 also works as the same way?
I don't have a C128 but 1084S manual says that C128 can be connected the same way as CGA (C128 can also be connected with S-video). Maybe 1902 also works as the same way?
The 1084S supports both analog and digital RGB. The 1902 is also dual RGB/composite, but doesn't support analog like the 1084S. It will probably display yellow instead of brown. The C128 manuals also say that color 6 is yellow.
My Tandy CM-11 also arrived. I connected it to my 5150 and it works fine. Brown is very hard to tell apart from red, however. I've heard that this is a problem on CGA monitors, although on your screenshot the brown and red can be easily seen apart. It gets a little easier to see after the monitor has been running for a bit and warmed up.