COSC 456Lesson 19: Laboratory 5

IBM PC Interfacing

• The parallel port is a 25-pin DB-25 (D-shaped) connector accessible from the back of the PC

• The expansion slot provides access to the address bus, data bus, several IRQ lines, clock signal, and several control lines

Parallel Port (DB-25 connector)

1 2 ... 13

14 15... 25

View is looking at female connector on the back of PC

DB-25 Pin Functions

• Pins 2 through 9 are the 8 data pins D0 through D7. Data Port = “base” address of the printer port(378)

• Pins 18 through 25 are ground pins

• Pins 1, 14, 16, and 17 are -strobe, -auto feed, initialize, and -select input. These are all outputs to the printer and accessed via the Control Port whose address is base + 2

• Pins 10, 11, 12, 13, and 15 are -acknowledge, busy, paper empty, select, and -error. These are outputs from the printer and accessed via the Status Port whose address is base + 1.

Moving data IN and OUT

IN Reads in the data from a peripheral device (I/O)

OUT Sends data out to a peripheral device(I/O)

MOV sends data to and from memory

IN and OUT the right way . . .

IN AL, 40H Data from port 40h is read into AL

OUT 40H, AL Data from AL is sent to port 40h

IN AL, 340H Illegal because 340 is > FF

MOV DX, 378 Data from port 378 is read into ALIN AL, DX

OUT DX, AL Data from AL sent to port 378

Memory Map

• 00000-003FF 1K Interrupt Vectors

• A0000 - BFFFF 128 KVideo RAM

• B8000-BBFFF 16K CGA

• A0000-AFFFF 64K VGA

• 00400-004FF 1/4 K BIOS Data Area

• F0000 - FFFFF 64 K BIOS ROM

I / O Map

• 00 - 1F DMA controller 8237A• 20 - 21 PIC1 (master) 8259A• 60 - 63 Keyboard controller 8042• 70 - 71 Real-time clock MC 146818• 80 - 83 DMA page register 74LS612• 1F0-1F8 Hard-disk controller• 200-207 Game adapter• 278-27F Parallel "printer" port 2 (LPT2)• 300-31F Prototype adapter for interfacing• 378-37F Parallel "printer" port1 (LPT1)• 3D0-3DF CGA / VGA controller• 3F0-3F7 "Floppy" disk controller• 3F8-3FF Serial port1 (asynchronous: COM1)