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Appendix
C251 User's Guide
Function Return Values
MCU registers pass function return values. The following table lists the return types and the registers used for each.
| Return Type | Register | Description |
|---|---|---|
| bit | Carry Flag | Single bit returned in the carry flag |
| char/unsigned char, 1-byte pointer |
R11 | Single byte type returned in R11 |
| int, unsigned int, 2-byte pointer |
WR6 | MSB in R6, LSB in R7. |
| long, unsigned long | DR4 | MSB in R4, LSB in R7 |
| float | DR4 | 32-Bit IEEE format: 'exponent' and 'sign' in WR4 |
| double | DR0, DR4 | 64-Bit IEEE format: 'exponent' and 'sign' in WR0 |
| 4-byte pointer | DR0 | MSB in R0, LSB in R3. |
For parameter passing to C51 functions; 3 byte pointers are returned in the registers R1/R2/R3. Refer to PARM51 or PARM251 for more information.
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