IO Ports Review

1
I/O Ports Review

• 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
A Note on HC11 Modes

• Why are ports B and C not available on Fox11?
• HC11 can operate in different modes
• Determined at reset
• Reads MODA and MODB pins at reset
• Status latched so a running program can detect
  mode

4
Modes

• Single Chip Mode
• All ports available as published
• No external address or data busses
• No external memory or memory mapped I/O available
• Expanded Mode
• Ports B and C used for external address and data
  bus
• WaUWaT (Whats Up With That)
• Port B is 8 bits out, Port C is 8 I/O

5
PC0 PC1 PC2 PC3 PC4 PC5 PC6 PC7 PB0 PB1 PB2 P
B3 PB4 PB5 PB6 PB7
6
I/O Techniques

• Weve used a couple of techniques
• Asynchronous
• Write and read memory/ports at will/convenience
• Works well for output (LED, LCD)
• Works for some inputs (static DIP Switches)
• Polled (input)
• Continuously read a port until desired value read
• Example reading key from keypad
• Works for input.but
• Keeps processor busy
• Not efficient for many applications

7
I/O with Handshaking

• Handshaking Additional I/O lines are connected
  between sender and receiver to regulate flow of
  data.
• Simple strobed I/O
• Sender tells the receiver that data is coming
• Full Handshaking
• Receiver tells sender that it is able to accept
  data
• Sender sends data
• Receiver tells sender that data was received (or
  not)
• HC11 offers some built-in handshaking
  functionality.

8
Simple Strobed Input

• Note Applies to Single Chip Mode
• Input on PORTCL (latched register for Port C
  inputs)
• Set PIOC (0x1002) bit 4 (HINDS handshaking
  mode) to 0
• Set PIOC bit 1 to indicate rising (1) or falling
  (0) edge trigger
• STRA input used to indicate when input data is
  available
• Read via STAF bit 7 of PIOC
• If bit 6 of PIOC is set, STAF will cause
  interrupt (more on this later)

9
Simple Strobed Output

• Output on PORTB
• Set PIOC (0X1002) bit 4 to 0 (same as input)
• STRB output pin active for 2 clocks when data
  written to Port B
• Bit 0 of PIOC indicates polarity of STRB (active
  high or low)

10
Timing Simple Strobe
11
Full Handshake Mode

• Used when both sender and receiver must agree on
  when data is sent
• PORTCL for data (1 to 8 bits)
• STRA input to HC11
• STRB output from HC11

12
Full Handshake Input

• STRB tells device HC11 is ready for data
• Device puts data on port
• Device pulls STRA high (or low) to signal data is
  there
• HC11 sees STAF bit set in PIOC
• Poll or use interrupts
• HC11 App reads PORTCL to get data.
• STRB tells device..

13
Full Handshake Output

• STRB tells device data is ready, and is set by
  writing to PORTCL
• Device pulls STRA high (or low) when data has
  been accepted
• Check STAF bit in PIOC