Z80 (TI-83+) stops working on CALL
assembly, calculator, texas-instruments, z80
Solution
Apparently, you are assembling to address 0080h. This can't be correct because the address range 0000h--3FFFh is locked to ROM page 0. Indeed, according to this example, you assemble to 4000h. So your problem is that your CALL is jumping into the firmware, not a part of your application.
Problem
Every time I assemble an application for the TI-83+ calculator (Z80 processor), it stops running at CALL. Here is an example ("Hello") — it starts running just fine, but the calculator freezes at the CALL instruction. Anything I put before CALL works just fine, and anything I put after doesn't run. This is a disassembly of the code, to show addresses rather than labels. I have "touched it up" to show DB lines where those fall in, to make it easier to read. I have never had this problem writing assembly "programs" (which are loaded into RAM). The only problems that I know of with running "applications" (which are kept in Flash ROM) are that they cannot be self-modifying, and that because paging is necessary, accessing data on a separate page is not possible. This is not self-modifying and only has one page... What have I done wrong? ``` 0080 218900 LD HL, 0089h 0083 cd9900 CALL 0099h ; --- App stops here 0086 c38f00 JP 008fh 0089 48656c6c6f00 DB "Hello", 0 008f fd360500 LD (IY+05h), 0 0093 ef RST 28h ; B_CALL ( 0094 364c DB 4C36h ; _ReloadAppEntryVecs) 0096 ef RST 28h ; B_CALL ( 0097 2740 DB 4027h ; _JForceCmdNoChar) --- App should end here 0099 7e LD A, (HL) ; --- Call goes to here 009a ef RST 28h ; B_CALL ( 009b 0445 DB 4504h ; _PutC) 009d fe00 CP 0 009f c8 RET Z 00a0 23 INC HL 00a1 18f6 JR 0099h ```