Jameco Electronics Rabbit 3000 - Manual (Page 251)

242 Rabbit 3000 Microprocessor
18.2 Reading and Writing I/O Registers
The Rabbit has two I/O spaces: internal I/O registers and external I/O registers.
18.2.1 Using Assembly Language
The fastest way to read and write I/O registers in Dynamic C is to use a short segment of
assembly language inserted in the C program. Access is the same as for accessing data
memory except that the instruction is preceded by a prefix (
IOI or IOE ) to indicate the
internal or external I/O space. For example:
// compute value and write to Port A Data Register
value=x+y
#asm
ld a,(value) ; value to write
ioi ld (PADR),a ; write value to PADR
#endasm
In the example above the IOI prefix changes a store to memory to a store to an internal
I/O port. The prefix ioe is used for writes to external I/O ports.
18.2.2 Using Library Functions
Dynamic C functions are available to read and write I/O registers. These functions are pro-
vided for convenience. For speed, assembly code is recommended. For a complete
description of the functions noted in this section, refer to the Dynamic C User’s Manual
or from the
Help menu in Dynamic C, access the HTML Function Reference or Function
Lookup options.
To read internal I/O registers, there are two functions.
int RdPortI(int PORT) ; // returns PORT, high byte zero
int BitRdPortI(int PORT, int bitcode); // bit code 0-7
To write internal I/O registers, there are two functions.
void WrPortI(int PORT, char *PORTShadow, int value);
void BitWrPortI(int PORT, char *PORTShadow, int value, int bitcode);
The external registers are also accessible with Dynamic C functions.
int RdPortE(int PORT) ; // returns PORT, high byte zero
int BitRdPortE(int PORT, int bitcode); // bit code 0-7
int WrPortE(int PORT, char *PORTShadow, int value);
int BitWrPortE(int PORT, char *PORTShadow, int value, int bitcode);
In order to read a port the following code could be used:
k=RdPortI(PADR); // returns Port A Data Register