Texas Instruments 99/4A - Page 60

TABLE 7
GROM MEMORY MAR
ADDRESS
TYPE OF INSTRUCTION
9800
9802
9C00
9C02
READ GROM DATA
READ GROM ADDRESS
WRITE GROM DATA
WRITE GROM ADDRESS
As can be seen, address A14 distinguishes between an address and data
instruction. Distinction between read and write instructions is made
by DBIN and the different addresses. This is done because when
writing data or address information, the 9900uP executes a dummy read
which would otherwise influence the address counter in the GROM.
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