B&B Electronics Parallel Port Input/Output Converter PPIO - Manual (Page 20)

18 PPIO2899 Manual
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104
C
ONTROLLING THE
PPIO U
SING
C
The PPIO disk includes three source code files as an example
of using the PPIO with the C programming language. PPIO.C is the
main routine of the example program. PPIOFUNC.C contains the
routines for communicating with the PPIO. PPIOFUNC.H contains
the function prototypes and definitions for use by PPIOFUNC.H and
PPIO.C. In the rest of this section, we assume that you know the C
programming language. Consult your reference manuals if you need
help with the language.
PPIOFUNC.H makes some definitions used in the rest of this
section.
#define Status_Address Base_Address+1
#define Control_Address Base_Address+2
typedef enum { false=0, true=1 } boolean;
The module, PPIOFUNC.C, handles communication with the
parallel port. It defines three variables that all functions inside the
module can access. They are defined as:
unsigned char Input_Byte;
unsigned char Output_Byte;
unsigned int Base_Address;
No function outside the module can directly access these
variables. Functions outside the module call functions within the
module to modify and return the value of these variables.
The function, Set_Start(), sets the variables Base_Address and
Output_Byte. It also sets up the initial state of the parallel port. The
function is defined as:
void Set_Start(unsigned int Address, unsigned char Init)
{
Base_Address = Address;
Output_Byte = Init;
outport(Base_Address, Output_Byte);
}
This function must be the first one used, because all other functions
assume that variable, Base_Address, has been set.