Question about registers in 16F628A, banks

[kcn]

In one of Nigel's tutorials (Tutorial 6.1 to be exact), he defines in his code

		cblock	0x20			;start of general purpose registers
			count			;used in looping routines
			count1			;used in delay routine
			counta			;used in delay routine
			countb			;used in delay routine
			LoX
			Bit_Cntr
			Cmd_Byte
			Dev_Byte
			Timer_H
			Flags
			Flags2
			tmp1			;temporary storage
			tmp2
			tmp3

			templcd			;temp store for 4 bit mode
			templcd2
			lcdtmp
	
			Adr_Lo			; EEPROM memory address to be accessed
			Adr_Hi
			DAT_VAL
			_N
			InputByte		; byte read from EEPROM is stored in this register
			Data_Page		; EEPROM page, 0-7
			OutputByte		; used for holding byte to be output to EEPROM
			I2Cflags		; flag bit register
		endc

Is each one of these "variables" (to sort of speak), exactly one byte?

Are these "variables" only accessible when you are in bank 0?

If the cblock 0x20 were changed to cblock 0xA0, would the "variables"
only be accessible when you are in bank 1?

Suppose I executed the following code

        movlw 0x20
        movwf fsr
next    clrf indf
        incf fsr
        btfss fsr, 2
        goto next

would the effect of this code basically set count, count1, counta, and countb all to zero? Would this only work when I am in bank 0?

Thank you.

kcn

 

[Mike - K8LH]

Hi again kcn,

Code:

      cblock   0x20         ;start of general purpose registers
         count         ;used in looping routines
         count1         ;used in delay routine
         counta         ;used in delay routine
         countb         ;used in delay routine
         LoX
         Bit_Cntr
         Cmd_Byte
         Dev_Byte
         Timer_H
         Flags
         Flags2
         tmp1         ;temporary storage
         tmp2
         tmp3

         templcd         ;temp store for 4 bit mode
         templcd2
         lcdtmp
   
         Adr_Lo         ; EEPROM memory address to be accessed
         Adr_Hi
         DAT_VAL
         _N
         InputByte      ; byte read from EEPROM is stored in this register
         Data_Page      ; EEPROM page, 0-7
         OutputByte      ; used for holding byte to be output to EEPROM
         I2Cflags      ; flag bit register
      endc

Is each one of these "variables" (to sort of speak), exactly one byte?

Yes, each variable is one byte...

Are these "variables" only accessible when you are in bank 0?

Yes and no... You can access them by name in operands when in Bank 0... You can access them indirectly using the FSR and INDF registers with the STATUS register IRP bit = 0 (you can indirectly access 000..0FF with IRP=0 and access 100..1FF with IRP=1)...

If the cblock 0x20 were changed to cblock 0xA0, would the "variables"
only be accessible when you are in bank 1?

Yes and no... You can access them by name in operands when in Bank 1... You can access them indirectly using the FSR and INDF registers with the STATUS register IRP bit = 0 (you can indirectly access 000..0FF with IRP=0 and access 100..1FF with IRP=1)...

Suppose I executed the following code
Code:

        movlw 0x20
        movwf fsr
next    clrf indf
        incf fsr
        btfss fsr, 2
        goto next

would the effect of this code basically set count, count1, counta, and countb all to zero? Would this only work when I am in bank 0?

Yes, this code would clear locations 20h through 23h... You can access 256 contiguous locations using indirect addressing... Locations 000h through 0FFh with the STATUS register IRP bit = 0 and locations 100h through 1FFh with IRP = 1... Pretty wierd, huh?

Regards, Mike