Create assembler_tms9900_ti99_4a.asm

Hello World for TI-99/4a computer with TMS9900 CPU

assembler_tms9900_ti99_4a.asm

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+
+* Hello World for TI-99/4a computer with TMS9900 CPU
+* by Frog ( http://frog.enlight.ru )
+* 15 April 2016
+*
+****************************************************************************
+
+        DEF     START
+
+WRKSP   EQU     >8300
+
+VDPWD   EQU     >8C00           * VDP RAM write data
+VDPWA   EQU     >8C02           * VDP RAM read/write address
+
+
+START   LIMI    0               * disable interrupts
+        LWPI    WRKSP           * set default workspace
+
+* set VDP RAM start address (low and high byte)
+
+        LI      R0,>0000
+        ORI     R0,>4000
+        SWPB    R0
+        MOVB    R0,@VDPWA
+        SWPB    R0
+        MOVB    R0,@VDPWA
+
+        LI      R1,HELLOWORLD   * ascii string address
+        LI      R2,12           * total chars
+
+NEXTCHAR
+        MOVB    *R1+,@VDPWD     * put next char on screen
+        DEC     R2
+        JNE     NEXTCHAR
+
+LOOPBACK
+        JMP LOOPBACK            * stop and do nothing
+
+
+HELLOWORLD
+        TEXT 'HELLO WORLD!'     * string data
+        BYTE 0
+
+        END