Sample Asm code for eZ80

boot_eZ80.asm

; =========================================================================
; Minimal eZ80 Assembly Boot Code 
; Targets: eZ80F91 / General eZ80 Series
; =========================================================================

    ASSUME  ADL = 1             ; Instruct assembler to output 24-bit ADL opcodes

    ORG     $000000             ; Power-On Reset Vector

reset_vector:
    DI                          ; Disable interrupts during hardware setup
    JP.L    init_system         ; Long Jump to force 24-bit addressing transition

    ORG     $000066             ; Non-Maskable Interrupt Vector
nmi_vector:
    RETN

; =========================================================================
; Hardware Register Definitions (eZ80F91 Spec)
; =========================================================================
UART0_RBR   EQU     $C0         ; Receiver Buffer Register
UART0_THR   EQU     $C0         ; Transmitter Holding Register
UART0_DLL   EQU     $C0         ; Divisor Latch LSB
UART0_DLM   EQU     $C1         ; Divisor Latch MSB
UART0_IER   EQU     $C1         ; Interrupt Enable Register
UART0_FCR   EQU     $C2         ; FIFO Control Register
UART0_LCR   EQU     $C3         ; Line Control Register
UART0_LSR   EQU     $C5         ; Line Status Register

RAM_CTL     EQU     $B4         ; On-chip SRAM Control Register
SYSTEM_CTL  EQU     $B6         ; System Control Register

; =========================================================================
; System Initialization
; =========================================================================
init_system:
    ; 1. Enable On-Chip RAM (Assumes 8KB/16KB internal SRAM)
    LD      A, $C0              ; Enable internal SRAM, map to top of memory
    OUT0    (RAM_CTL), A

    ; 2. Initialize Stack Pointer 
    ; Using the top of the internal SRAM (e.g., $FFFFFF)
    LD      SP, $FFFFFF         

    ; 3. Setup UART0 (9600 Baud assuming a 50MHz System Clock)
    LD      A, $80              ; Enable Divisor Latch Access (DLAB)
    OUT0    (UART0_LCR), A
    
    LD      A, $45              ; Divisor Latch LSB ($0145 = 325 for 9600 baud)
    OUT0    (UART0_DLL), A
    LD      A, $01              ; Divisor Latch MSB
    OUT0    (UART0_DLM), A
    
    LD      A, $03              ; Reset DLAB, Set character length to 8 bits, 1 stop, No Parity
    OUT0    (UART0_LCR), A
    
    LD      A, $00              ; Disable UART interrupts
    OUT0    (UART0_IER), A

    ; 4. Main Application Entry Point
    LD      HL, msg_boot        ; Point to the string
    CALL    print_string

loop_forever:
    JR      loop_forever        ; Trap CPU here

; =========================================================================
; Helper Functions
; =========================================================================

; Prints a null-terminated string via UART0
print_string:
    LD      A, (HL)
    OR      A, A                ; Check if byte is null (\0)
    RET     Z                   ; If null, return
    
    CALL    uart_tx_byte        ; Send the byte
    INC     HL                  ; Move to next character
    JR      print_string

; Transmits a single byte in Register A via UART0
uart_tx_byte:
    PUSH    AF                  ; Save the character
tx_wait:
    IN0     A, (UART0_LSR)      ; Read Line Status Register
    AND     A, $20              ; Check THRE (Transmitter Holding Register Empty) bit
    JR      Z, tx_wait          ; If 0, buffer full; loop until clear
    
    POP     AF                  ; Restore character
    OUT0    (UART0_THR), A      ; Transmit byte
    RET

; =========================================================================
; Data Section
; =========================================================================
msg_boot:
    DB      "\r\n--- eZ80 System Booted Successfully ---\r\n", 0