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i am new to PIC programming. I am using MPLAB X + XC8 compiler. I have on a breadboard an PIC18F4550 connected to a HD44780 compatible LCD. Digging online i found out a routine to interface the PIC with the LCD controller, works ok on 8MHz internal osc.

LCD is connected to the PIC like this: RB0 = D4 RB1 = D5 RB2 = D6 RB3 = D7 RD5 = RS RD7 = E

In my code, all PORTB is used for Data lanes and from PORTD only RD5 and RD7 are defined for RS and E.

My question: How can i move RS and E pins to PORTB also , so the LCD uses a SINGLE PORT, not 2 ports. . Because if i define for example RS as RB4 and E as RB5 , the code that toggles the DATA lines is like this (PORTB = data_to_send) , so it toggles all PORTB pins , not just RB0..RB3 . How can i address/toggle a pin range (RB0..RB3) of a PORT and not the whole port?

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There is two methods you can use:

  1. Address individual pins. In XC8 you have such variables as LATBbits.LATB3 which you can set to 1 or 0 to turn an individual pin on or off.
  2. Use bitwise operators and masks. You can "or" and "and" bits together to turn chunks of a port on or off, such as LATB &= 0xF0 will turn off the lower 4 bits. LATB |= 0x03 will then turn the lowest two bits on without changing any other bits.
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Like Manjenko said you can use a mask, and this is probably the best option especially in the case of the PIC18 devices since they have a LAT register that will avoid any read-modify-write issue.

If you just want to update the 4 least significant bits with the value of the data variable you can do something like this:

LATB = LATB & 0xF0 | (data & 0x0F);

This will keep the 4 most significant bits and update just the 4 least significant bits.

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  • \$\begingroup\$ thanks , it worked like this. but i had no success with E (RB5) , i tried moving it to RB6 or 7 still crappy characters. So i moved them all on PORTD, so i have D4-D7 on RD0-RD3 and i left RS on RD5 and E on RD7, working perfect. \$\endgroup\$ – George Dima Nov 15 '14 at 20:12
  • \$\begingroup\$ Are you using the LAT registers to set individual bits like Manjeko suggested? You should use them instead of PORT registers, i.e. LATBbits.LATB5 instead of PORTBbits.RB5 for instance. \$\endgroup\$ – Bruno Ferreira Nov 15 '14 at 20:30
  • \$\begingroup\$ yes, of course, i always use LAT , but the issue with PORTB seems to be related to this PIC structure, i don't have the knowledge to understand what was wrong. Because for PORTD works and for PORTB no... i only set them with TRIS = 0 for output at startup, maybe for PORTB latest pins i must set other property also, cause i think something was disturbing communication of RB5 there... \$\endgroup\$ – George Dima Nov 15 '14 at 21:07
  • \$\begingroup\$ Do you have the programmer/debugger connected when you test? Since it uses the same pins it could be the issue. You cannot program it in debug mode if you use these pins. \$\endgroup\$ – Bruno Ferreira Nov 15 '14 at 21:12
  • \$\begingroup\$ yes, i have it connected by ICSP , but it's not the issue, ICSP uses only RB6&7 (so not RB5), but i tried it also with external power and same issue. \$\endgroup\$ – George Dima Nov 15 '14 at 21:15

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