C51: 80C517: Using the 517 Multiply / Divide Unit in Interrupts

Information in this article applies to:

• C51 Version 5.50
• C51 Version 6.00 Beta
• C51 Version 6.00

SYMPTOMS

Can I use the high-speed multiply/divide unit of the Infineon 80C517 in my main program and in an interrupt routine?

CAUSE

No. The 517 multiply/divide unit does not allow recursive use of the MDU indexes. The overhead of saving and restoring these registers would eliminate the advantage of the MDU. Therefore, the MDU may be used in the main program or an interrupt, but not both.

RESOLUTION

If you must use the MDU in an interrupt and in your main code, you must disable interrupts in your main code when you multiply and divide, and restore interrupts when your math routines are finished. This ensures that interrupts do not run while you access the MDU of the 517.

SEE ALSO

• C51: Using MDU_F120 and MDU_R515 in µVision

Last Reviewed: Thursday, February 25, 2021