University of Tehran 1 Interface Design Keyboard and Printer Omid Fatemi

University of Tehran 2 Typical Interface Design Connect ComputeConveyCooperate Sense Reality Touch Reality Connect Transform Embedded Systems Micros Assembler, C Real-Time Memory Peripherals Timers DMA PC interfaces HCI Busses Protocols Standards PCI IEEE488 SCSI USB & FireWire CAN

University of Tehran 3 Outline Keyboard design Key detection Keyboard buffer Centronics printer interface IO printer ports Parallel port types Interfacing LPT ports to various devices

University of Tehran 4 Keyboard Layout Linear layout –N input ports for N keys Matrix layout –2N ports (N input and N output) for N^2 keys

University of Tehran 5 Scanning and Identifying Micro controller Rows to output ports Columns to input ports Grounding rows Reading the columns Grounding one row Reading the columns

University of Tehran 6 Detection Algorithm

University of Tehran 7 Assembly Code

University of Tehran 8 PC Keyboard Micro controller (8042) –Microprocessor, RAM, EPROM, I/O ports Detection by 8042 Scan code assign Serial communication to motherboard –One start bit (0) –8 bits for scan code –Odd-parity bit –One stop bit (1) 74LS322 (serial-in-parallel-out SR) in motherboard to port A of 8255 (port 60H) In AT and later PCs another 8042 in motherboard

University of Tehran 9 PC Scan Codes Make (0-7FH and break (plus 80H)

University of Tehran 10 Advanced Scan Codes

University of Tehran 11 Status Bytes 0040:0017 H (first) 0040:0018 H (second)

University of Tehran 12 Printer Printer and Printer Interfacing

University of Tehran 13 Centronics printer interface 36-pin Grounds to reduce electrical noise (signal has its own ground return) Data lines Printer status signals Printer control signals Ground signals

University of Tehran 14 Pin Layout

University of Tehran 15

University of Tehran 16 Printer Connector

University of Tehran 17 Printer-PC Communication PC checks busy If not busy, PC puts 8-bit data PC activates #STROBE (.5 micro) Data must stay (.5 micro after STROBE) Printer assert busy After reading data printer asserts #ACKNLG (5 micro) De-assert busy

University of Tehran 18 I/O Base Address for LPT -d 0040:0008 LPT: 03BC, 0378, I/O ports –– LPT data lines –– LPT status lines –– LPT control lines

University of Tehran 19 Printer’s Ports

University of Tehran 20 BIOS: INT 17H AH=0 –Print a character –AL: ASCII –DX: LPT number –AH returns status AH=1 –Initialize AH=2 –Get the status Printer time out? –20 seconds (-d 0040:0078)

University of Tehran 21 Special Characters

University of Tehran 22 Inner Working of INT 17

University of Tehran 23 Printer Timing

University of Tehran 24 Buffering Ports

University of Tehran 25 Using Parallel Ports

University of Tehran 26 Stepper Motor

University of Tehran 27 Selected Problems 5, 6, 8 22, 28, 32, 43

University of Tehran 28 Summary