E5frog: 1 revision

2012-11-16T21:22:46Z

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Admin at 21:16, 20 November 2004

2004-11-20T21:16:21Z

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The data counter is a 16-bit [[register]] in the [[F8]] which allows access to data stored in ROM. Unlike other [[CPU]]s, like the 6502, the F8 doesn't allow you to directly load and store data into a byte in memory, using a single [[opcode]]; the F8 only provides opcodes to load and store data in memory from the address pointed to by the data counter, or '''DC'''.

There are two DC's on the F8, called DC0 and DC1. DC1 can't be used by any opcode, but can only be switched with DC0 using '''XDC'''. This however is helpful when you want to move portions of data from one location in memory to another. To load data using the DC, you can use the opcode '''LM''', which loads a byte from memory into the [[accumulator]]. To store data, use the opcode '''ST''', which stores the accumulator into that address in memory. Alternatively, with the contents of that addres you can add, [[AND (binary)|AND]], [[OR (binary)|OR]], or [[XOR (binary)|XOR]] it with the accumulator. Each of these operations will increase DC0 when used.

You can manipulate the address stored by DC0 by swapping it with the [[register]] Q or H, adding the contents of the accumulator to it, swapping DC0 with DC1, or loading an immediate address using '''DCI'''. And as stated before, any opcodes using the DC will increase it after it's finished.

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Data counter - Revision history

E5frog: 1 revision

Admin at 21:16, 20 November 2004