Using General I/O Ports to Drive LCD Displays

Transcription

1 Using General I/O Ports to Drive LCD Displays D/N:HA0092E Introduction In certain special cases, where it is required to reduce costs and where demand on the I/Os are low, users often require to use standard I/O pins to drive LCD displays. This project is in response to this need and can be used as a basis for actual applications. Description 1. When using I/O ports to drive an LCD display, the I/O port can only have 3 kinds of standard signal, therefore it is only possible to implement 1/2 bias. 2. When testing using the HT46R22 (24-pin type) for control, the circuit is as shown in Fig. 1. Pins PA0 to PA3 and PB3 and PB5 are used to control SEG0~SEG5, while PB3, PB6 and PB7 are used for COM0 to COM2. 1

2 +, ' 2 E + 5 A C 5 A C 5 A C 5 A C! 5 A C " 5 A C # + +! ' 9! ' 9! ' 9 8,, # 9! " # $ % & ' 2 * # ) # 2 * " ) " 2 )! 2., 2 ) 2 ) 2 ) 2 *! )! 2 * ) 2 * ) 2 * ) * $ ) $ 2 * % ) % 2 ) " ) # ) $ 5, ) 2 ) % ,, 4-5 2, " $ 4 " 2 E "! ' & % $ # "! " 0 9 ) %!!! ' 9 Fig The I/O ports have three standard setup methods. For the COM port, select the internal pull high resistor and also connect external pull-low resistors. For example, when the I/O port changes from a high output, to an input and then to a low output, this will provide an output voltage of VDD, 1/2 VDD, and 0V respectively. 4. The display waveform is shown in figure 2. For the LCD to illuminate, the corresponding LCD area s COM and SEG should have a voltage of ±VDD for illumination to occur. If the corresponding voltage is 0V or 1/2 VDD then no illumination will take place. If an alternating plus or minus VDD voltage is applied to the LCD area then the life of the display can be extended. If the LCD glass is 3V then VDD = 3V, if the LCD glass is 5V, then VDD = 5V. 5. The example program uses minutes and will display from 00 to 59 after which it will repeat. 2

3 , K H E C = H A I A JF K I A ) HEL A H K JF K JI H = F A H = A , I A C A JI + I E@ A I > A E C K EJ O +, I A C A JI + I E@ A > A E C EJ O +, I A C A JI + I E@ A > A E C EJ O +, I A C A JI + I E@ A > A E C EJ +, I A C A JI + I E@ A I > A E C EJ +, I A C A JI + I E@ A I > A E C EJ +, I A C A JI + I E@ A I > A E C EJ +, I A C A JI + I E@ A I > A E C EJ 0 ) A ) HEL A H K JF K JI Fig The two LCDs 7-seg corresponding connections are as shown in Table 1. Seg0 Seg1 Seg2 Seg3 Seg4 Seg5 COM0 1e 1d 1c 2e 2d 2c COM1 1b 1a 2b 2a COM2 1g 1f 2g 2f Table 1 3

4 Program Example Using General I/O Ports to Drive LCD Displays ;FILE NAME: IO_LCD ;MCU: HT46R22 ;MASK OPTION: WAKE-UP: PA6,PA7 ; PULL-HIGH: PA,PB,PC ; IIC: DISABLE ; PFD: DISABLE ; PWM: DISABLE ; WDT: ENABLE ; CLRWDT: ONE ; WDT CLOCK SOURCE: T1 ; WDT TIME OUT SELECT: WDT CLOCK SOURCE/32768 ; LVR: DISABLE ; OSC: CRYSTAL ; SYSVOLT: 3.0V ; SYSFRAG: 4000kHZ ;AUTHOR: RADOME ;HISTORY: include Ht46r22.inc include Micro.inc IO_data.section data acc_bk db? status_bk db? pa_bk db? pb_bk db? pbc_bk db? pulse_count db? display_temp db? display_temp0 db? display_temp1 db? display_temp2 db? number0 db? number1 db? number2 db? msecond db? second db? minute db? segment0 equ pa_bk.0 segment1 equ pa_bk.1 segment2 equ pa_bk.2 segment3 equ pa_bk.3 segment4 equ pb_bk.4 segment5 equ pb_bk.5 4

5 com0 equ pb_bk.3 com0_ctrl equ pbc_bk.3 com1 equ pb_bk.6 com1_ctrl equ pbc_bk.6 com2 equ pb_bk.7 com2_ctrl equ pbc_bk.7 IO_code.section code org 0000h init org 0004h ;External Interrupt reti org 0008h ;Timer Interrupt timer_int org 0020h ;Initializers init: intc0 intc1 tmrc set set msecond second minute pulse_count display_temp display_temp0 display_temp1 display_temp2 number0 number1 number2 a, b pa,a pa_bk,a a, b pac,a pb pb_bk a, b pbc,a pbc_bk,a 5

6 a, b pc,a pcc pd pdc a, b intc0,a a,94 tmr,a a, b tmrc,a ;Main main_loop: wdt a,minute add a,bcd_table tblp,a tabrdl number2 a,number2 and a,0f0h swap acc number0,a a,number2 and a,0fh number1,a a,number0 display_temp0,a a,number1 display_temp1,a a,number2 display_temp2,a main_loop 6

7 ;Interrupt timer int: ;2592us push ;COM Operation Mode com_pulse: inc pulse_count a,pulse_count sub a,7 snz c $+3 a,1 pulse_count,a a,pulse_count $+2 com1_out_high $+2 com1_out_low $+2 com2_out_high $+2 com2_out_low com0_out_low com0_out_high: com0_ctrl set com0 set com1_ctrl set com2_ctrl segment_pulse com0_out_low: com0_ctrl com0 set com1_ctrl set com2_ctrl segment_pulse 7

8 com1_out_high: set com0_ctrl com1_ctrl set com1 set com2_ctrl segment_pulse com1_out_low: set com0_ctrl com1_ctrl com1 set com2_ctrl segment_pulse com2_out_high: set com0_ctrl set com1_ctrl com2_ctrl set com2 segment_pulse com2_out_low: set com0_ctrl set com1_ctrl com2_ctrl com2 ;SEGMENT Operation Mode segment_pulse: ; segment0_out: a,display_temp0 add a,number_table tblp,a tabrdl display_temp a,display_temp and a, b inc acc $+2 segment0_000 $+2 segment0_001 $+2 segment0_010 8

9 $+2 segment0_011 $+2 segment0_100 $+2 segment0_101 segment0_111 segment0_110 segment0_000: segment0_001: segment0_010: segment0_011: segment0_100: segment0_101: segment0_110: segment0_111: a,com_000_table segment0_next a,com_001_table segment0_next a,com_010_table segment0_next a,com_011_table segment0_next a,com_100_table segment0_next a,com_101_table segment0_next a,com_110_table segment0_next a,com_111_table segment0_next: add a,pulse_count tblp,a tabrdl acc segment0 sz acc set segment0 ; segment1_out: a,display_temp 9

10 and a, b inc acc $+2 segment1_000 $+2 segment1_001 $+2 segment1_010 $+2 segment1_011 $+2 segment1_100 $+2 segment1_101 segment1_111 segment1_110 segment1_000: segment1_001: segment1_010: segment1_011: segment1_100: segment1_101: segment1_110: segment1_111: a,com_000_table segment1_next a,com_001_table segment1_next a,com_010_table segment1_next a,com_011_table segment1_next a,com_100_table segment1_next a,com_101_table segment1_next a,com_110_table segment1_next a,com_111_table 10

11 segment1_next: add a,pulse_count tblp,a tabrdl acc segment1 sz acc set segment1 ; segment2_out: acc sz display_temp.7 set acc.0 inc acc $+2 segment2_000 $+2 segment2_001 $+2 segment2_010 $+2 segment2_011 $+2 segment2_100 $+2 segment2_101 segment2_111 segment2_110 segment2_000: segment2_001: segment2_010: segment2_011: a,com_000_table segment2_next a,com_001_table segment2_next a,com_010_table segment2_next a,com_011_table segment2_next 11

12 segment2_100: segment2_101: segment2_110: segment2_111: a,com_100_table segment2_next a,com_101_table segment2_next a,com_110_table segment2_next a,com_111_table segment2_next: add a,pulse_count tblp,a tabrdl acc segment2 sz acc set segment2 ; segment3_out: a,display_temp1 add a,number_table tblp,a tabrdl display_temp a,display_temp and a, b inc acc $+2 segment3_000 $+2 segment3_001 $+2 segment3_010 $+2 segment3_011 $+2 segment3_100 $+2 segment3_101 12

13 sdz segment3_000: segment3_001: segment3_010: segment3_011: segment3_100: segment3_101: segment3_110: segment3_111: acc segment3_111 segment3_110 a,com_000_table segment3_next a,com_001_table segment3_next a,com_010_table segment3_next a,com_011_table segment3_next a,com_100_table segment3_next a,com_101_table segment3_next a,com_110_table segment3_next a,com_111_table segment3_next: add a,pulse_count tblp,a tabrdl acc segment3 sz acc set segment3 ; segment4_out: a,display_temp and a, b inc acc $+2 segment4_000 $+2 segment4_001 13

14 $+2 segment4_010 $+2 segment4_011 $+2 segment4_100 $+2 segment4_101 segment4_111 segment4_110 segment4_000: segment4_001: segment4_010: segment4_011: segment4_100: segment4_101: segment4_110: segment4_111: a,com_000_table segment4_next a,com_001_table segment4_next a,com_010_table segment4_next a,com_011_table segment4_next a,com_100_table segment4_next a,com_101_table segment4_next a,com_110_table segment4_next a,com_111_table segment4_next: add a,pulse_count tblp,a tabrdl acc segment4 sz acc set segment4 ;

15 segment5_out: acc sz display_temp.7 set acc.0 inc acc $+2 segment5_000 $+2 segment5_001 $+2 segment5_010 $+2 segment5_011 $+2 segment5_100 $+2 segment5_101 segment5_111 segment5_110 segment5_000: segment5_001: segment5_010: segment5_011: segment5_100: segment5_101: segment5_110: a,com_000_table segment5_next a,com_001_table segment5_next a,com_010_table segment5_next a,com_011_table segment5_next a,com_100_table segment5_next a,com_101_table segment5_next a,com_110_table segment5_next 15

16 segment5_111: a,com_111_table segment5_next: add a,pulse_count tblp,a tabrdl acc segment5 sz acc set segment5 ;Output COM&SEGMENT output_com_segment: a,pb_bk pb,a a,pbc_bk pbc,a a,pa_bk pa,a ;Time inc msecond a,msecond sub a,192 snz c timer_end msecond timer_end: pop reti inc second a,second sub a,120 snz c timer_end second inc minute a,minute sub a,60 snz c timer_end minute 16

17 ;Table org 0700h number_table: ; gbefadc b ; b ; b ; b ; b ; 4" b ; b ; b ; b ; b ; b ; - a b ; b ; com_000_table: 0 1,0,1,0,1,0 com_001_table: 0 1,0,1,0,0,1 com_010_table: 0 0,1,1,0,1,0 com_011_table: 0 0,1,1,0,0,1 com_100_table: 0 1,0,0,1,1,0 com_101_table: 0 1,0,0,1,0,1 com_110_table: 0 0,1,0,1,1,0 com_111_table: 0 0,1,0,1,0,1 17

18 bcd_table: 00h,01h,02h,03h,04h,05h,06h,07h,08h,09h 10h,11h,12h,13h,14h,15h,16h,17h,18h,19h 20h,21h,22h,23h,24h,25h,26h,27h,28h,29h 30h,31h,32h,33h,34h,35h,36h,37h,38h,39h 40h,41h,42h,43h,44h,45h,46h,47h,48h,49h 50h,51h,52h,53h,54h,55h,56h,57h,58h,59h 60h,61h,62h,63h,64h,65h,66h,67h,68h,69h 70h,71h,72h,73h,74h,75h,76h,77h,78h,79h 80h,81h,82h,83h,84h,85h,86h,87h,88h,89h 90h,91h,92h,93h,94h,95h,96h,97h,98h,99h end 18