RCA COSMAC Operator's Manual page 20

MACHINE LANGUAGE PROGRAMMING (cont'd)
The instructions given above are examples of UTZ
"calling sequences". Only the simplest information
sufficient to get the user started in some elementary
coding has been presented here. To intelligently use
all of the facilities available from UTZ, a programmer
should be familiar with the details provided n pp.Z6-3l
("UTZ Features and Calling Sequences"). In particular,
the TYPE linkage described above is not necessarily the
best to use. Other TYPE linkages which result in a
higher output rate and which use arguments passed via
registers are discussed in the section cited above.
Given the ability to execute simple typewriter I/O
functions, the user is now able to code elementary test
programs to further exercise the Microkit. As a simple
example, consider the routine described in the
COS~~C
Microprocessor Manual (p.40) to read two bytes, compare
them and output the "larger" of the two. The routine
given there must be modified to exhibit register usage
compatible with the UTZ READ and TYPE calling sequences.
Further, the I/O instructions of that program must be
replaced with calls to the appropriate UTZ typewriter
interface routines. Figure Z, below, gives an example
of this program appropriately modified.
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