12 Chapter 2: TI-83 Plus Specific Information
TI-83 Plus Developer Guide Third Release May 28, 2002
RST Routines
The Z80 restart instruction, RST, can be used in place of B_CALL for some entry points.
Using the RST instruction only takes one byte of ROM space as opposed to three bytes
for a B_CALL. There are five routines set to use this method of access. These were
chosen because of high-frequency use in the operating system.
• RST rMov9ToOP1 used instead of B_CALL Mov9ToOP1
• RST rFindSym used instead of B_CALL FindSym
• RST rPushRealO1 used instead of B_CALL PushRealO1
• RST rOP1ToOP2 used instead of B_CALL OP1ToOP2
• RST rFPAdd used instead of B_CALL FPAdd
Details on these routines can be found in this chapter or in the System Routine
Documentation.
System RAM Areas
The details about system RAM follow.
System Flags
This area of RAM is used for bit flags. The TI-83 Plus accesses these flags through the
Z80’s IY register. The IY register is set to the start of this flag area and does not
change, resulting in easy bit manipulation.
Example:
SET trigDeg,(IY+trigFlags) ; set to degree angle mode
trigFlags is the byte offset from the start of the flag area.
Some system flags that an application might use are listed in Table 2.1, along with
information needed to support basic ASM programming on the TI-83 Plus.
The values for these symbols are located in the include file, TI83plus.inc.
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