The DR_ApReadBlock and DR_ApWriteBlock functions access the process I/O data area of the card. The offset and size parameters specify what portion of the buffer area to transfer, and is dependent on the field configuration. Typically, field data is always mapped to the beginning of the block (offset of 0) and is continguous up to the number of bytes defined by the field device (slave) configuration. The output process data buffer is mapped as buffer 0, while 1 will access the input process data buffer.

The DR_ApReadControl and DR_ApWriteControl functions access the control parameter blocks of the card. Only buffer 2 is valid for CIF cards, which provides access to the protocol parameters.

The control parameters for the Hilscher Fieldbus card use the following structure (see file cif_api.h):

typedef struct {
     unsigned char	Mode;
     unsigned char	reserved1;
     unsigned char	Format;
     unsigned short	WatchdogTime;
     unsigned char	reserved5[3];
     unsigned char	reserved8[8];
} cif_ApParms_t;

The control parameters do vary with the specific fieldbus protocol and additional structure definitions can be found in the cif_api.h file.

Access to the control data is accomplished via buffer 2 with a length of 16, using the functions DR_ApReadControl and DR_ApWriteControl, as follows:

DR_ApReadControl (dev, 2, 0, 16, &control, &error)
DR_ApWriteControl (dev, 2, 0, 16, &control, &error)

It is recommended that reserved bytes be set to 0. Most protocols reserve the last 11 bytes, so the length may be shortened to 5, depending on the protocol. Note that a read of the control parameters may return only zero data from some cards.

The components of the control structure are defined as follows:

The handshake modes available are:

Not all modes are available for all protocols.

The available storage formats are:

After writing the control block, the system must do a WARM reset before the changes will take effect (see the cardReset command in the Device Driver for Hilscher CIF Cards manual).

The DR_ApReadStatus function accesses the status blocks of the card. Only buffer 2 is valid for CIF cards, which provides master status as well as field device (slave) status and diagnostic information.

The status of the Hilscher Fieldbus Card is read from buffer 2 with a length of 64, using the function DR_ApReadStatus, as follows:

DR_ApReadStatus (dev, 2, 0, 64, &status, &error)

The offset and length are ignored. Status is a structure of type cif_ApState_t (see the file cif_api.h) and is defined as follows:

typedef struct {
    unsigned char	global_bits;
    unsigned char	bus_status;
    unsigned char	err_rem_addr;
    unsigned char	err_rem_event;
    unsigned char	reserved[28];
    unsigned char	state [16];
    unsigned char	diag [16];
} cif_ApState_t;

where: