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Debugging
187
It is important to note that interrogating an I/O register (R4, R5, R6, or R7) causes an input
I/O bus cycle, using the current Pa register contents as the interface address. See Chapter 7 for
details on the effects of such an action.
Patching
Patching is the practice of changing the contents of memory locations without re-assembling.
Patching as a standard procedure does not come highly recommended in the programming
world. Nonetheless, there are circumstances which arise that occasionally suggest patching as
the most profitable course of action.
To change a particular location in memory in the 9835A/B is not difficult. The statement to use
is-
"r ("""
E::: {assembled location}
""r"()
{octal expression}
After execution of the statement, the specified {assembled location} contains the specified octal
value.
Changing the contents of a register is a common use of this facility. However, it should be
remembered that attempting to change the contents of the I/O registers (R4, R5, R6, or R7)
causes an output I/O bus cycle to occur, using the Pa register for the interface address. See
Chapter 7 for details on the effects of such an action.
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