I am using the SPI to access a couple of 20 & 24 bit A/D converters which have some digital status bits preceding the reading. I already have some C code written (for another CPU) that defines the incoming data structure as a unsigned long. The Keil compiler, however, says I must use char or integer size bit fields. Is there an easy way around this without having to hand code the byte manipulation code manually?
Here are some C51 declarations for a pair of cascaded (obsolete) MC14489 LED display drivers. In an external FPGA is an SPI interface that the CPU writes to in 8-bit (unsigned char) chunks, using the unions to get the bytes. This is implemetation dependent. // // LED Display // #define LED_DATA ((unsigned char volatile xdata *)0xe080) // LED data register (WR) #define LED_ENABLE_OFF ((unsigned char volatile xdata *)0xe081) // negate SPI ENABLE signal (any data) (WR) typedef struct { unsigned char leds_enable :1; unsigned char leds_not_hex_1 :1; unsigned char leds_not_hex_2 :1; unsigned char leds_not_hex_3 :1; unsigned char leds_not_hex_4 :1; unsigned char leds_not_hex_5 :1; unsigned char leds_special_123 :1; unsigned char leds_special_45 :1; unsigned char not_used_1 :8; unsigned char not_used_2 :8; unsigned char digs_enable :1; unsigned char digs_not_hex_1 :1; unsigned char digs_not_hex_2 :1; unsigned char digs_not_hex_3 :1; unsigned char digs_not_hex_4 :1; unsigned char digs_not_hex_5 :1; unsigned char digs_special_123 :1; unsigned char digs_special_45 :1; } led_ctrl_struct; typedef struct { unsigned char low_pwr :1; // first four bits are bank 5 nibble for leds unsigned char hi_pwr :1; unsigned char not_used_1 :2; unsigned char leds_dp_pos :3; // next four bits are decimal point/brightness control for leds unsigned char leds_bright :1; unsigned char ready :1; // next four bits are bank 3 nibble for leds unsigned char at_power :1; unsigned char not_used_2 :2; unsigned char spare_1 :1; // next four bits are bank 4 nibble for leds unsigned char spare_2 :1; unsigned char not_used_3 :2; unsigned char not_used_4 :4; // next four bits are bank 1 nibble for leds (not used) unsigned char remote_on :1; // next four bits are bank 2 nibble for leds unsigned char arc :1; unsigned char not_used_5 :2; unsigned char digit_4 :4; // next four bits are bank 5 for digits unsigned char digs_dp_pos :3; // next four bits are decimal point/brightness for digits unsigned char digs_bright :1; unsigned char digit_2 :4; // next four bits are bank 3 for digits unsigned char digit_3 :4; // next four bits are bank 4 for digits unsigned char not_used_6 :4; // next four bits are bank 1 for digits (not used) unsigned char digit_1 :4; // last four bits are bank 2 for digits } led_data_struct; typedef union { unsigned char ledc[4]; led_ctrl_struct ledcs; } led_ctrl_union; typedef union { unsigned char ledd[6]; led_data_struct ledds; } led_data_union;