AR# 2726: XBLOX: ACCUM - effects of LOAD on C_OUT and OVFL
AR# 2726
XBLOX: ACCUM - effects of LOAD on C_OUT and OVFL
説明
Keywords: XBLOX, ACCUM, LOAD, C_OUT, OVFL
Urgency: standard
General Description: What is the effect on the C_OUT and OVFL outputs of asserting LOAD on the XBLOX ACCUM macro?
ソリューション
The synchronous LOAD function of the XBLOX ACCUM macro is implemented via a 2-to-1 multiplexer. The LOAD signal acts as the select line on the mux. When LOAD is high, the mux passes the B input to the ACCUM register; when LOAD is low, the mux passes the ADD/SUB value to the ACCUM register.
LOAD has no direct effect on the C_OUT and OVFL outputs. During a LOAD operation, the C_OUT and OVFL outputs will continue to reflect the carry out and overflow status of the ADD/SUB logic. However, since LOAD affects Q_OUT, which drives the A input of the ADD/SUB logic, it does affect C_OUT and OVFL indirectly.