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Applications of AVR single chip controllers AT90S, ATtiny, ATmega and ATxmega Experimental board with an ATtiny24/44/84 and an LCD

Experimental board with an ATtiny24/44/84 and a LCD

• An ATtiny24/44/84 with an attached standard LCD and base routines in assembler make the rest of the development a simple matter.
• Based on your needs up to four I/O pins can be used for the following purposes:
  • as normal in- or out-put pins, or
  • as AD converter input pins, or
  • as analog comparators, or
  • as PCINT inputs to generate PCINT interrupts, or
  • as counter input pin for the 8 bit timer/counter TC0.
• The small 40-by-50 mm PCB can be connected with a 6 pin flat ribbon cable with external parts on e.g. a breadboard. The power supply of 5.0 or 3.3 V (depending from the LCD's needs) can be provided via the cable or can be attached to two pins.
• As LCD all types with 1, 2 or four lines by 8, 16, 20 or 24 characters can be used and can be configured by changing software constants.
• The LCD include routines provide ready-to-use software for initiation, for displaying text and binary numbers, either as 8- or 16-bit binary, in hexadecimal or in decimal format. The two routines work with a clock frequency of up to 20 (lcd.inc) resp. 8 MHz (tn24_lcd_busy.inc).

0 Overview

1. Hardware
2. Mounting
3. Software

1 Hardware

1.1 Scheme of the board

1.2 Parts list

1.3 Example applications

11. here is an 8- and a 16-bit binary counter described that advances each time the controller is switched on, reads from/writes to EEPROM and displays the number in decimal format on LCD,
12. here an infrared remote control receiver is described that analyses control signals with diverse tools, an Attiny13 remote control transmitter and an Attiny24 IR data receiver with LCD,
13. here a frequency counter for digital and small-amplitude analog signals and for measuring inductivities is decribed,
14. here a voltage meter for voltages of up to 20 V, for currents up to several amperes DC and for temperatures inside the controller is described.

2 Mounting

2.1 PCB

2.2 Mechanical mounting

3 Software

1. A universal version, that handles all different connections of LCDs, including 8 bit versions, and
2. a special version that is adapted only to this hardware and that handles only the ATtiny24 and this 4 bit version.

3.1 Universal version lcd.inc

• LCD access with 8- or 4-bit data bus (define with the constants LcdBits=8 or LcdBits=4),
• when using a 4 bit data bus select whether the bus is connected to the upper or lower nibble of the port (with the constant Lcd4High=0 for the lower or Lcd4High=1 for the upper nibble),
• automatic adaption to clock frequencies above 1 MHz (define the constant clock in Hz),
• access either with waiting for the LCD's busy flag or with wait cycles (define the constant LcdWait=0 for busy or LcdWait=1 for wait cycles),
• the control pins of the LCD {E, RS, RW} can be tied to whatever port and portpins and do not have be within the same port (define those with the constants pLcdCnnO, pLcdCnnD, bLcdCnnO and bLcdCnnD, with nn={E, RS, RW}),
• can be adapted to LCD sizes of 1x{8, 16, 20, 24} or 2x{16, 20, 24} or 4x{16, 20, 24} (define this with the constants LcdLines={1, 2, 4} and LcdColumns={8, 16, 20, 24}).
• all constants that are required for the selected operating mode are checked by the assembler if those are defined and correct (simplified debugging),
• for the list of constants and for the design of text masks of all above mentioned LCD sizes templates are given in the include file that can be copy-and-pasted to the source code, and after editing, semicolons can be removed to activate those lines,
• optional conversion and display of binary numbers as
  • decimals with two, three or five digits (define the constant LcdDecimal),
  • hexa decimals with two or four digits (define the constant LcdHex).
• protecting and restoring of registers used (except R16 and ZH:ZL) by PUSH and POP,
• Time and code size optimized by extensive use of conditional assembling (.IF and .IFDEF directives).

3.1.1 Standard parameter set for tn24_lcd

; Standard parameter set of properties/definitions
  .equ clock = 1000000 ; Clock frequency of controller in Hz
; LCD size:
  .equ LcdLines = 4 ; Number of lines (1, 2, 4)
  .equ LcdCols = 20 ; Number of characters per line (8..24)
; LCD bus interface
  .equ LcdBits = 4 ; Bus size (4 or 8)
  ; If 4 bit bus:
    .equ Lcd4High = 1 ; Bus nibble (1=Upper, 0=Lower)
  .equ LcdWait = 0 ; Access mode (0 with busy, 1 with delay loops)
; LCD data ports
  .equ pLcdDO = PORTA ; Data output port
  .equ pLcdDD = DDRA ; Data direction port
; LCD control ports und pins
  .equ pLcdCEO = PORTB ; Control E output port
  .equ bLcdCEO = PORTB2; Control E output portpin
  .equ pLcdCED = DDRB ; Control E direction port
  .equ bLcdCED = DDB2 ; Control E direction portpin
  .equ pLcdCRSO = PORTB ; Control RS output port
  .equ bLcdCRSO = PORTB0 ; Control RS output portpin
  .equ pLcdCRSD = DDRB ; Control RS direction port
  .equ bLcdCRSD = DDB0 ; Control RS direction portpin
; If LcdWait = 0:
  .equ pLcdDI = PINA ; Data input port
  .equ pLcdCRWO = PORTB ; Control RW output port
  .equ bLcdCRWO = PORTB1 ; Control RW output portpin
  .equ pLcdCRWD = DDRB ; Control RW direction port
  .equ bLcdCRWD = DDB1 ; Control RW direction portpin
; If you need binary to decimal conversion:
  ;.equ LcdDecimal = 1 ; If defined: include those routines
; If you need binary to hexadecimal conversion:
  ;.equ LcdHex = 1 ; If defined: include those routines
; If simulation in the SRAM is desired:
  ;.equ avr_sim = 1 ; 1=Simulate, 0 or undefined=Do not simulate
;

3.1.2 Standard routines of the include file

; ***********************************************
; *  L C D   I N T E R F A C E  R O U T I N E S *
; ***********************************************
;
; +-------+----------------+--------------+
; |Routine|Function        |Parameters    |
; +-------+----------------+--------------+
; |LcdInit|Inits the LCD   |Ports, pins   |
; |       |in the desired  |              |
; |       |mode            |              |
; +-------+----------------+--------------+
; |LcdText|Displays the    |Z=2*Table     |
; |       |text in flash   |  address     |
; |       |memory starting |0x0D: Next    |
; |       |with line 1     |      line    |
; |       |                |0xFF: Ignore  |
; |       |                |0xFE: Text end|
; +-------+----------------+--------------+
; |LcdSram|Display the text|Z=SRAM-Address|
; |       |in SRAM         |R16: number of|
; |       |                |    characters|
; +-------+----------------+--------------+
; |LcdChar|Display charac- |R16: Character|
; |       |ter on LCD      |              |
; +-------+----------------+--------------+
; |LcdCtrl|Output control  |R16: Control  |
; |       |byte to LCD     |     byte     |
; +-------+----------------+--------------+
; |LcdPos |Set position on |ZH: Line 0123 |
; |       |the LCD         |ZL: Col 0..   |
; +-------+----------------+--------------+
; |LcdSpec|Generate special|Z: 2*Table    |
; |       |characters      |   address    |
; +-------+----------------+--------------+
; |    S W I T C H   L C D D E C I M A L  |
; +-------+----------------+--------------+
; |LcdDec2|Convert to two  |R16: Binary   |
; |       |decimal digits  |     8 bit    |
; +-------+----------------+--------------+
; |LcdDec3|Convert to three|R16: Binary   |
; |       |decimal digits, |     8 bit    |
; |       |supp. leading 0s|              |
; +-------+----------------+--------------+
; |LcdDec5|Convert to five |Z: Binary     |
; |       |decimal digits, |   16 bit     |
; |       |supp. leading 0s|              |
; +-------+----------------+--------------+
; |      S W I T C H   L C D H E X        |
; +-------+----------------+--------------+
; |LcdHex2|Convert to two  |R16: Binary   |
; |       |digits in hex   |     8 bit    |
; +-------+----------------+--------------+
; |LcdHex4|Convert to four |Z: Binary     |
; |       |digits in hex   |   16 bit     |
; +-------+----------------+--------------+
;

3.1.3 Used flash memory

3.2 Special version tn24_lcd_busy.inc

• LcdInit: The I/O pins of the LCD and the LCD is initiated. Application is demonstrated here with a 4 line by 20 characters per line LCD. A start message is shown (left picture),
  
  
  
  and, following an adjustable delay time (constant cLcdDelay in the main source code in multiples of 250 ms) an output mask is displayed (right picture, in German).
• LcdText, LcdTextC: A text in a flash table, for which the doubled address is given in the register pair ZH:ZL, is displayed from line 1 on (LcdText) or starting at the current LCD address (LcdTextC) until the selected line count (1, 2 or 4) is exceeded or an end marker is reached. The control characters 0x0D (Carriage return plus linefeed) and 0xFE (End of text) control the output). As you always have to adjust the text in the .db directive to hold an even number of characters you can add 0xFF as ignored dummy character. Output ends on exceeding the number of lines or triggered by 0xFE.
• LcdSram: The text im SRAM, for which the address is given in register pair XH:XL, with the number of characters to be displayed is handed over in register rmp (R16), is displayed at the LCD position handed over in register pair ZH:ZL (ZH: Line 0..3, ZL: Column 0..cLcdColumns-1).
• LcdLine, LcdLine1, LcdLine2, LcdLine3, LcdLine4: LcdLine adjusts the LCD's position to the beginning of the line that is handed over in register rmp (R16, 0..cLcdLines-1). When calling LcdLine1, LcdLine2, ..., the same happens without parameter handing-over.
• LcdPos: Adjusts the position of the LCD to the line given in register ZH (0..cLcdLines-1) and the column in register ZL (0..cLcdColumns-1).
• LcdChar: The ASCII character (0x20..0x7F) or the special character (0x00..0x07) given in register rmp (R16) is displayed on LCD at the current LCD position.
• LcdCtrl: The control byte in register rmp (R16) is written to the control register of the LCD.
• LcdChars: The table in flash memory, on which the doubled address in ZH:ZL points, and which holds a table with encoded special characters is written to the character generator in the LCD. Up to eight special characters (0..7) can be defined.

• The main source code has to init the stack (in ATtiny24 and ATtiny44 SPL, in ATtiny84 SPH and SPL), because calling and diverse push and pops inside the routines would otherwise fail).
• In the main source code the constant clock should be set to the correct controller clock frequency in Hz (up to 8000000 Hz), because the I/O interface to the LCD depends from that (specified duration of the LCD Enable pulse).
• In the main source code set the constant cLcdDly to the desired delay between the opening screen and the output mask. Otherwise assembling fails with an error message.
• When the program is interrupt-driven make sure that initiating the LCD happens prior to interrupt enabling. The lengthy delays during LCD init would conflict with interrupt handling if the interrupt sets handling flags to be reacted on.
• In the main source code define the register rmp as R16 (or above).
• Make sure that the temporarily used registers R0, R1, R2 and ZH:ZL (plus XH:XL when using text display from SRAM) are not used inside interrupt service routines.

3.2.1 Number conversion and display routines

3.2.2 Example application of the code without Interrupts

3.2.3 Example application with interrupts

3.2.4 Required flash storage