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.