AR# 2726

XBLOX: ACCUM - effects of LOAD on C_OUT and OVFL

Description

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?

Solution

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.
AR# 2726
Date 05/19/1999
Status Archive
Type General Article