It was thus said that the Great Marvin once stated: It supports two modes that CGA doesn't: 320x200 16 color and 640x200 4 color, in addition to the other CGA modes. The 320x200 16 mode isn't quite EGA in layout though - the palette registers only support 2 bits of red, 2 of green and 2 of blue, and the layout of the pixels follows (more or less) the CGA standard than the EGA bitplanes. Each byte held two pixels (four bits per pixel) and the memory layout was: 0x0000: 2000 bytes of screen information, each line 40 bytes, lines evenly divisible by 0 0x2000: 2000 bytes of screen information, each line 40 bytes, line % 4 == 1 0x4000: 2000 bytes of screen information, each line 40 bytes, line % 4 == 2 0x6000: 2000 bytes of screen information, each line 40 bytes, line % 4 == 3 The 620x200 4 color mode was similarly laid (layed?) out, only there were four pixels per byte (2 bits per pixel). -spc (Although with proper programming, the CGA could support 160x100 16 colors (or was it 160x200?))

All this talk about the PCJr is really inspiring....I want to get mine out of the closet and fire it up! Could someone post a schematic of the power supply kludge with the 17v. center-tapped transformer? Also how would I go about replacing the plug in daughtercard memory board, which was trashed when I got the machine? Kirk Scott dynasoar(a)mindspring.com

It's enhanced CGA. The IBM monitor _was_ the 5153 CGA monitor with an adapter cable (or at least it was when my Techref was printed - it gives the wirelist of the adapter and the schematics of the 5153). The video circuitry in the PC-jr can output a few more modes that a CGA card can't (320*200 in 16 colours, etc), but the monitor is a normal CGA one. -- -tony ard12(a)eng.cam.ac.uk The gates in my computer are AND,OR and NOT, not Bill

It was thus said that the Great Jeff Hellige once stated: For the normal CGA modes, yes. But for the 320x200x16 and 640x200x4 no. For some reason, when in those modes, they did not appear at the standard CGA address in the IBM PCjr, which made programming for those modes on the PCjr real fun (gotta love the way MS-DOS can't deal with non-contiguous memory). In the PCjr, the video memory could reside anywhere in the first 128K of RAM, but there was circuitry to echo that to the standard CGA addresses. And due to the video memory sharing main memory, the PCjr wasn't as fast as the PC (that, and due to lack of DMA). When programming those modes under MS-DOS, I had to boot a particular setup where I knew the address of the video, which left me less memory to work with MS-DOS, since MS-DOS was loaded PAST the video memory (which if I recall, meant I lost something like 64 or 96K of RAM - oh, the video memory couldn't reside just anywhere, there were alignment restrictions. Sigh). -spc (Funny that the Tandy's were more compatible than the PCjr ... )