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GMS81C2112 Datasheet(PDF) 29 Page - Hynix Semiconductor |
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GMS81C2112 Datasheet(HTML) 29 Page - Hynix Semiconductor |
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29 / 107 page 
GMS81C2112/GMS81C2120 JUNE. 2001 Ver 1.00 23 8.2 Program Memory A 16-bit program counter is capable of addressing up to 64K bytes, but this device has 20K bytes program memory space only physically implemented. Accessing a location above FFFFH will cause a wrap-around to 0000H. Figure 8-5, shows a map of Program Memory. After reset, the CPU begins execution from reset vector which is stored in address FFFEH and FFFFH as shown in Figure 8-6. As shown in Figure 8-5, each area is assigned a fixed loca- tion in Program Memory. Program Memory area contains the user program. Figure 8-5 Program Memory Map Page Call (PCALL) area contains subroutine program to reduce program byte length by using 2 bytes PCALL in- stead of 3 bytes CALL instruction. If it is frequently called, it is more useful to save program byte length. Table Call (TCALL) causes the CPU to jump to each TCALL address, where it commences the execution of the service routine. The Table Call service area spaces 2-byte for every TCALL: 0FFC0H for TCALL15, 0FFC2H for TCALL14, etc., as shown in Figure 8-7. Example: Usage of TCALL The interrupt causes the CPU to jump to specific location, where it commences the execution of the service routine. The External interrupt 0, for example, is assigned to loca- tion 0FFFAH. The interrupt service locations spaces 2-byte interval: 0FFF8H and 0FFF9H for External Interrupt 1, 0FFFAH and 0FFFBH for External Interrupt 0, etc. Any area from 0FF00H to 0FFFFH, if it is not going to be used, its service location is available as general purpose Program Memory. Figure 8-6 Interrupt Vector Area Interrupt Vector Area D000H FEFFH FF00H FFC0H FFDFH FFE0H FFFFH B000H TCALL area LDA #5 TCALL 0FH ; 1BYTE INSTR UCTIO N :; INSTEAD O F 3 BYTES :; NO RM AL CALL ; ;TABLE CALL ROUTINE ; FUNC_A: LDA LRG0 RET ; FUNC_B: LDA LRG1 RET ; ;TABLE CALL ADD. AREA ; ORG 0FFC0H ; TCALL ADDRESS AREA DW FUNC_A DW FUNC_B 1 2 0FFE0H E2 Address Vector Area Memory E4 E6 E8 EA EC EE F0 F2 F4 F6 F8 FA FC FE - - Serial Communication Interface Basic Interval Timer - - - Timer/Counter 0 Interrupt - External Interrupt 0 - RESET Vector Area External Interrupt 1 Watchdog Timer Interrupt "-" means reserved area. NOTE: Timer/Counter 1 Interrupt - A/D Converter |
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