Chapter 4. Address. data. Input / Output Programming. Simplified Z80 System Architecture. Memory. program. data. Z80 I/O Programming

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1 Simplified Z80 System Architecture I/O Port Address Addr Memory Addr 0000 Chapter 4 Input / Output Programming FF I/O Port Decoder IORQ RD WR 8 Z80 CPU data MEMRQ RD WR 8 Address Decoder program data FFFF I/O Select Signal Z80 I/O Interfacing 8-bit I/O Address = 00h FFh (256 I/O) 8-bit wide data transfer Shared data bus among multiple I/Os Port numbers are hardware-defined Access via IN / OUT instructions Decoder Address Z80 Data 10h 12h 14h. 18h Z80 I/O Programming Use system call (if available) via RST instruction Example: ET-Board provides system calls to I/O devices: Keyboard LCD Display Speaker Printer Tape Real-time Clock Serial Communication ORG 2000 LD A, 17h ;call to system function 17h (Clear LCD display) RST 10h ;jump to subroutine LD A, 18h ;call to system function 18h (turn off cursor) RST 10h ;jump to subroutine HALT LED Array LCD Matrix Switch Speaker

Liquid Crystal Display (LCD) Liquid crystal (LC) is an organic

structure An electric field is used to control the molecules LCD

by 20 X char up to 8 lines X 80) Integrated controller The display

select register Data lines (DB7-DB0) used to transfer data and

seen Liquid Crystal Display Interface Connector Graphic LCD Text

pixel i.e., 128 x 64 dots User is able to control pixel

2 Liquid Crystal Display (LCD) Liquid crystal (LC) is an organic substance that has both a liquid form and a crystal molecular structure An electric field is used to control the molecules LCD cheap and easy way to display text Various configurations (1 line by 20 X char up to 8 lines X 80) Integrated controller The display has two register command register data register By RS you can select register Data lines (DB7-DB0) used to transfer data and commands Background of LCD can be seen Background of LCD cannot be seen Liquid Crystal Display Interface Connector Graphic LCD Text mode / Graphic mode display capability Resolution is defined in pixel i.e., 128 x 64 dots User is able to control pixel individually Displaying graphic image requires pixel mapping Available as with or without backlight model

Line x 16 Characters LCD Interfacing Initialize LCD Z80 HD44780 Pinout 8 data pins D7:D0 RS: Data or Command Register Select R/W: Read or Write E: Enable (Latch data) Load ASCII code of a character

3 LCD Model LCD consists of two internal RAM units; Display RAM, Character generator RAM (CG) Display RAM corresponds to memory at each column. Display RAM stores ASCII code of characters to be displayed LCD Model CG RAM stores a table of ASCII codes of characters There are preloaded characters and free space for user-defined characters 1 Line x 16 Characters LCD Interfacing Initialize LCD Z80 HD44780 Pinout 8 data pins D7:D0 RS: Data or Command Register Select R/W: Read or Write E: Enable (Latch data) Load ASCII code of a character to desired display RAM Data Bus RS Register Select RS = 0 Command Register RS = 1 Data Register R/W = 0 Write, R/W = 1 Read E Enable Used to latch the data present on the data pins. Next character? D0 D7 Bi-directional data/command pins. Alphanumeric characters are sent in ASCII format. END Not shown in actual connection

Controlling LCD display is to control signal sent to HD44780 controller LCD Commands The LCD s internal controller can accept several commands and modify the display accordingly.

4 Controlling LCD display is to control signal sent to HD44780 controller LCD Commands The LCD s internal controller can accept several commands and modify the display accordingly. Such as: Clear screen Return home Decrement/Increment cursor After writing to the LCD, it takes some time for it to complete its internal operations. During this time, it will not accept any new commands or data. We need to insert time delay between any two commands or data sent to LCD LCD Simulator Simulation of LCD module (HD44780 Controller) User on/off control signal individually while watching output being shown on display

5 Two options for programming LCD (ET-Board) Use system call Custom LCD subroutine ET-Board 4.0 System call related to LCD Two options for programming LCD (ET-Board) Use system call Custom LCD subroutine lcd_init equ 0Ah lcd_disp equ 16h Syscall equ 10h ORG 2000 LD A, lcd_init ;call LCD initializing subroutine RST Syscall ;jump to subroutine LD HL, msg ;HL = pointer to string LD A, lcd_disp ;call to system function 16h (display string) RST Syscall ;jump to subroutine HALT msg: db Hello World!!,00 ; string must terminate with NULL (00h) Two options for programming LCD (ET-Board) Use system call Custom LCD subroutine INIT_LCD: ; Subroutine used to initialize LCD to 8-bit interface, 2 lines, 57 font size LD A, b CALL WR_INSTR ;call write instruction to LCD routine LD A, b CALL WR_INSTR LD A, b CALL WR_INSTR RET Conclusion System call can be used to ease I/O programming I/O (if any) Consult user manual how to utilize them (usually via RST instruction) One useful output device is LCD which is programmable ET-Board provides system routines for LCD Programming LCD requires proper signals sent to LCD modules according to instruction described in the datasheet WR_INSTR: ; Write instruction to LCD CALL BUSY ;check if LCD is busy or not OUT (WR_COMM), A ;clear to send RES 6, A RET

6 No problem can withstand the assault of sustained thinking. ~Voltaire

AN1745. Interfacing the HC705C8A to an LCD Module By Mark Glenewinkel Consumer Systems Group Austin, Texas. Introduction

AN1745. Interfacing the HC705C8A to an LCD Module By Mark Glenewinkel Consumer Systems Group Austin, Texas. Introduction Order this document by /D Interfacing the HC705C8A to an LCD Module By Mark Glenewinkel Consumer Systems Group Austin, Texas Introduction More and more applications are requiring liquid crystal displays