M. Amer Iqbal Qureshi
PulsOut Rowrst,2 ' give a pulse on row reset pin, to select row 0 Loop: SHOut
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- PulsOut
| PulsOut Rowrst,2
' give a pulse on row reset pin, to select row 0 Loop: SHOut SER,SRCLK, lsbfirst ,[%11111110,%11111111,%11111111,%11111111] ' send data on serial pin ON PulsOut Latch,4 DelayMS 500 SHOut SER,SRCLK, lsbfirst ,[%11111111,%11111111,%11111111,%11111111] ' send data on serial pin OFF PulsOut Latch,4 DelayMS 500 GoTo Loop End Now lets make the entire row turn ON, and then select the next row, till all 8 rows are show, one after the other. Dim i As Byte Loop: PulsOut Rowrst,2 ' give a pulse on row reset pin, to select row 0 For i=0 To 7 SHOut SER,SRCLK, lsbfirst ,[%00000000,%00000000,%00000000,%00000000] PulsOut Latch,4 DelayMS 500 PulsOut RowClk,2 Next i GoTo Loop This code sends all columns on data, then waits for 500ms, and then gives a short pulse on RowClk pin. This pulse will advance the row selection to next row, and the same data is sent again. The whole process is repeated 8 times, till the last row, number 7 is displayed. After this the row counter is reset to select row 0 and the entire process is repeated. So far so good. Now begins the real fun. Notice that we have made a delay of 500ms between rows. If we reduce this time, rows will be displayed quicker,. Fine, if we go on reducing the time, a state will reach when our eyes will not be able to perceive the individually on rows, rather they will see all rows ON! When in fact, still, one row is being turned on, at a time. Try following timings, in place of 500. begin with 500 as in above program and then try, 300, 200, 100, 50, 20, 10, 5, 2 . A delay of 2ms will produce the best result, you will see an absolutely flicker free display. As shown in figure 9. All 256 LEDs appear to be ON. Fig. 7 Entire Row is ON Fig. 9 All lights appearing to be ON Teach Yourself PIC Microcontrollers | www.electronicspk.com | 142 When in fact one row, of 32 are on at a time. This is due to persistence of vision. Displaying Characters As you have seen that, you can play with these bits, to show anything you want. Text characters are similarly not a big problem. However you will need to make a table or list of character maps, that you will send to the display. Most characters can be easily mapped in 5 x 7 array. However for simplicity of our work, we will design them as an 8 x 8 matrix. Selecting this matrix, will also be helpful in making some other more feature rich graphics. Lets see how to work Up. We are going to design letter ‘A’. The adjacent fig shows the character map. The numbers in gray column, are in hexadecimal, equivalent. 1 for Off and 0 for On. Now we can store this character in bytes of memory. EEPROM on microcontroller is a good place to keep such maps, which once defined, have to be read in by the program. We have used EData command to store the codes for each row byte for the letter in EEPROM. The size of table which can be stored will depend upon the EEPROM of your microcontroller. If a larger table is required you can use an external EEPROM. The loop fills in the appropriate bytes of display memory by reading the associated bitmap image from EEPROM. The index of letters to be displayed are stored in an array z[4]. Number 0 is for letter ‘A’ as it is defined in position 0 in EEPROM, and number 1 is for ‘B’ as it is in position 1 in EEPROM. Notice how the position of first byte is calculated. E3 DD DD DD C1 DD DD DD tải về 3.06 Mb. Chia sẻ với bạn bè của bạn:
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