The TIA (as seen by the programmer)

2.0 The Registers

All instructions to the TIA are achieved by addressing and writing to various registers in the chip. A key point to remember is data written in a register is latched an retained until altered by another write operation into that register. For example, if the color register for a player is set for red, that player will be red every time it is drawn until that color register is changed. All of the registers are addressed by the microprocessor as part of the overall RAM/ROM memory space.

All registers have fixed address locations and pre-assigned address names for handy reference. Many registers do not use all 8 data bits, and some registers are used to strobe or trigger events. A strobe register executes its function the instant it is written to (the data written is ignored). The only registers the microprocessor can read are the collision registers and input port registers. These registers are conveniently arranged so that the data bits of interest always appear as data bits 6 or 7 for easy access.

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