Register Descriptions; Access To Ubc Registers - Hitachi SH7751 Hardware Manual

20.2

Register Descriptions

20.2.1

Access to UBC Registers

The access size must be the same as the control register size. If the sizes are different, a write will
not be effected in a UBC register write operation, and a read operation will return an undefined
value. UBC register contents cannot be transferred to a floating-point register using a floating-
point memory load instruction.
When a UBC register is updated, use either of the following methods to make the updated value
valid:
1. Execute an RTE instruction after the memory store instruction that updated the register. The
updated value will be valid from the RTE instruction jump destination onward.
2. Execute instructions requiring 5 states for execution after the memory store instruction that
updated the register. As the SH7751 Series executes two instructions in parallel and a
minimum of 0.5 state is required for execution of one instruction, 11 instructions must be
inserted. The updated value will be valid from the 6th state onward.
Rev. 3.0, 04/02, page 754 of 1064