IO Ports

1
I/O Ports

• Standard HC11 Ports
• PORTA 0x1000 3 out, 3 in, 2 I/O
• PORTB 0x1004 8 out
• Not available on Fox 11
• PORTC 0x1004 8 I/O
• Not available on Fox 11
• PORTD 0x1008 6 I/O (2 used for serial port)
• PORTE 0x100A 8 in
• Fox 11 Ports
• PORTB 0x1404 8 out to LEDs
• PORTC 0x1403 8 in from DIP switches
• PORTF 0x1401 8 out for LCD, SW Reset

2
Using I/O Ports

• Dedicated input and output pins are generally
  ready to use at reset
• Configurable pins (I/O) are generally set to
  input at reset, and must be configured for output
  by writing (a 1) to the corresponding data
  direction register
• DDRC 0x1007
• DDRD 0x1009
• DDRA7 bit 7 of 0x1026
• DDRA3 bit 3 of 0x1026
• Different ports support various other peripherals
  which are configured via various other registers.
• When port pins are configured for alternate
  functions, corresponding bit in port control
  register generally has no effect.
• Reference Manual is best resource.

3
Reading Keypad

• On Fox11 keypad
• columns are wired to port D pins 25 (output)
• rows wired to port E pins 0-3 (input)
• rows have pull-up resistors
• We need to have all Port D pins high, a set low
  one-by-one to scan keypad.

4
Reading Keypad

• Sequence
• Set DDRD bit 2-5 to output mode
• Do not want to mess with pins we are not using
• Want to do a read-modify-write
• LDAA DDRD
• ORA 0b00111100
• STAA DDRD
• or use BSET, but only works direct and indexed
• Set PORTD25 high
• Set PRTD2 low
• Check PORTE03, if any zeros, row and column
  found.
• If no zeros, set PORTD2 high and PORTD3 low.
• Check PORTE03,
• Repeats until all four columns have been pulled
  low

5
ASCII

• Pronounced ASS-KEY
• Standard character encoding for terminals and
  communication
• In GNU assembler char gives ASCII value
• LDAA 0 ? loads 48, or 0x30 into ACCA

6
Example Convert an 8-bit number to ASCII string

• General routine
• num/100 -gt quotient and remainder
• convert quotient to ASCII
• remainder/10 -gt quotient and remainder
• convert quotient to ASCII
• convert remainder to ASCII

7

• convert number at some num to ascii and
  display on LCD line 2
• ldy buffer set iY to buffer to receive ascii
  string
• clra
• ldab somenum
• ldx 100
• idiv Quotient is in X, remainder in D.
• Convert Quotient to ASCII
• xgdx q now in D (b actually since we know it
  is lt3
• ldaa 0x30
• aba ASCII value now in A
• staa 0,y
• iny
• xgdx remainder back in D (B)
• ldx 10
• idiv
• xgdx q now in D
• ldaa 0x30
• aba
• staa 0,y

8
BCD ? ASCII

• A little easier
• Store number if necessary
• Shift right 4 times (equivalent to /10)
• Convert to ASCII (add 0x30)
• Restore number
• Mask off upper nibble (and 0x0F)
• Convert to ASCII
• Done

9

• ldy buffer set iY to buffer to receive ascii
  string
• ldaa somenum
• do upper nibble first
• lsra
• lsra
• lsra
• lsra
• ldab 0x30
• aba ASCII value now in A
• staa 0,y
• iny
• ldaa somenum
• anda 0b00001111
• ldab 0x30
• aba
• staa 0,y
• iny
• clr 0,y write a null
• ldx buffer Display the second line