jsin@maui.cs.ucla.edu (Jonghoon Sin) (11/15/88)
I'm posting this for a friend:
I've built some hardware that interfaces to the PC through three 8 bit
I/O ports. I've used a 8255 with a couple of other TTL/LS chips as glue.
My questions are:
1. In a minimal PC configuration (256K RAM, 1 floppy/controller,
monochrome card) what port addresses are typically unoccupied?
Is the area 03C0 to 03CF safe to use?
2. I'm finding that the IOW' line is asserted about
every 15us. Is this normal? What's the PC doing?
I should mention that I'm using a 4.77/8Mhz Taiwanese clone and
not a True Blue PC.matthew@sunpix.UUCP ( Sun NCAA) (11/18/88)
In article <17932@shemp.CS.UCLA.EDU>, jsin@maui.cs.ucla.edu (Jonghoon Sin) writes: > I'm posting this for a friend: > > I've built some hardware that interfaces to the PC through three 8 bit > I/O ports. I've used a 8255 with a couple of other TTL/LS chips as glue. > My questions are: > > 1. In a minimal PC configuration (256K RAM, 1 floppy/controller, > monochrome card) what port addresses are typically unoccupied? > Is the area 03C0 to 03CF safe to use? > > 2. I'm finding that the IOW' line is asserted about > every 15us. Is this normal? What's the PC doing? > > I should mention that I'm using a 4.77/8Mhz Taiwanese clone and > not a True Blue PC. The IBM Personal Computer Hardware Reference Library back to the rescue again. The writer of this article, and of another one I recently read, should get some useful info out of this post. Below is a copy of the I/O address map on page 2-23 of the above manual (notice, that due to incomplete decoding, that I/O space within the range $000 thru $0FF is consumed by the motherboard). Hex-Range 9 8 7 6 5 4 3 2 1 0 device ---------------------------------------------------------- 00-0f 0 0 0 0 0 Z A3 A2 A1 A0 DMA Chip 8237-2 20-21 0 0 0 0 1 Z Z Z Z A0 INTERUPT 8259A 40-43 0 0 0 1 0 Z Z Z A1 A0 TIMER 8253-5 60-63 0 0 0 1 1 Z Z Z A1 A0 PPI 8255A-5 80-83 0 0 1 0 0 Z Z Z A1 A0 DMA PAGE REGS AX 0 0 1 0 1 Z Z Z Z Z NMI MASK REG CX 0 0 1 1 0 Z Z Z Z Z RESERVED EX 0 0 1 1 1 Z Z Z Z Z RESERVED ---------------------------------------------------------- 200-20F 1 0 0 0 0 0 A3 A2 A1 A0 GAME I/O ADAPTER 278-27F 1 0 0 1 1 1 1 A2 A1 A0 RESERVED 2F8-2FF 1 0 1 1 1 1 1 A2 A1 A0 RESERVED 378-37F 1 1 0 1 1 1 1 Z A1 A0 PARALLEL PRTR PORT 3B0-3BF 1 1 1 0 1 1 A3 A2 A1 A0 IBM MONOCHROMATIC DISPLAY/ PARALLEL PRINTER ADAPTER 3D0-3DF 1 1 1 1 0 1 A3 A2 A1 A0 COLOR GRAPHICS ADAPTER 3F8-3FF 1 1 1 1 1 1 1 A2 A1 A0 TP RS-232-C CD -- Matthew Lee Stier (919) 469-8300| Sun Microsystems --- RTP, NC 27560| "Wisconsin Escapee" uucp: {sun, rti}!sunpix!matthew |
vo@micomvax.UUCP (Vladimir Orlt) (11/30/88)
In article <275@greens.UUCP> matthew@sunpix.UUCP ( Sun NCAA) writes: >In article <17932@shemp.CS.UCLA.EDU>, jsin@maui.cs.ucla.edu (Jonghoon Sin) writes: >> 2. I'm finding that the IOW' line is asserted about >> every 15us. Is this normal? What's the PC doing? It's probably the MEMR' line you were looking at. The PC is doing a memory refresh cycle every 15us or so. If you did see the 'IOW line strobing regularly, it could have been a clock-type interrupt being serviced; the IOW' activity could be due to the CPU accessing the PIC. Vlad the Re-mailer ...!philabs!micomvax