Motorola 68HC08 Hello World

I have a MC68HC908JB8 that I know exactly diddly about. This is an attempt to piece together a simple "Hello World" program in assembly. I want to be able to hook the chip up to a USB port and read the device name. I'm working primarily from the code from the usb-ir-boy project. This code is heavily commented in hopes that I can gain a clue.

I spent several hours trying to understand the SCI interface before noticing that my microcontroller doesn't have one.

SCC1 = $0013
This is a variable definition. This is the address of the Serial Communication Interface (SCI) Control Register #1. From the documentation, this register is:
$0013Read: LOOPS ENSCI TXINV M WAKE ILTY PEN PTY
Write:
SCC2 = $0014
SCI Control Register #2:
$0014Read: SCTIE TCIE SCRIE ILIE TE RE RWU SBK
Write:
SCC3 = $0015
SCI Control Register #3:
$0015Read: R8 T8 R R ORIE NEIE FEIE PEIE
Write:
SCS1 = $0016
SCI Status Register #1:
$0016Read: SCTE TC SCRF IDLE OR NF FE PE
Write: R R R R R R R R
SCS2 = $0017
SCI Status Register #2:
$0017Read: 000000 BKF RPF
Write: R R R R R R R R
SCDR = $0018
SCI Data Register: Read and write data from the SCI
SCBR = $0019
SCI Baud Rate Register:
$0019Read:00 SCP1 SCP0 SCR2 SCR1 SCR0
Write:
PPG = $001E
PLL Programming Register (PPG):
$001ERead: MUL7 MUL6 MUL5 MUL4 VRS7 VRS6 VRS5 VRS4
Write:
MOR = $001F
Mask Option Register (MOR):
$001FRead:0 ROMSEC LVIRSTD LVIPWRD SSREC COPL STOP COPD
Write: R R R R R R R
UCR0 = $003B
UCR1 = $003C
USB Control Register 1:
$003CRead: T1SEQ STALL1 TX1E FRESUM TP1SIZ3 TP1SIZ2 TP1SIZ1 TP1SIZ0
Write:
UCR2 = $0019
USB Control Register 2:
$0019Read: T2SEQ STALL2 TX2E RX2E TP2SIZ3 TP2SIZ2 TP2SIZ1 TP2SIZ0
Write:
UCR3 = $001A
USB Control Register 3:
$001ARead: TX1ST 0 OSTALL0 ISTALL1 0 PULLEN ENABLE2 ENABLE1
Write: TX1STR
UCR4 = $001B
USB Control Register 4:
$001BRead: 00000 FUSBO FDP FDM
Write:
USR0 = $003D
USB Status Register 0:
$003DRead: R0SEQ SETUP 0 0 RP0SIZ3 RP0SIZ2 RP0SIZ1 RP0SIZ0
Write:
USR1 = $003E
USB Status Register 1:
$003ERead: R2SEQ TXACK TXNAK TXSTL RP2SIZ3 RP2SIZ2 RP2SIZ1 RP2SIZ0
Write:
UE0D0 = $0020
USB Endpoint 0 Data Register 0: First of eight read/write data registers (UE0D7 = $0027)
UE1D0 = $0028
USB Endpoint 1 Data Register 0: First of eight write only data registers (UE1D7 = $002F)
UE2D0 = $0030
USB Endpoint 2 Data Register 0: First of eight read/write data registers (UE2D7 = $0037)
UIR0 = $0039
USB Interrupt Register 0:
$0039Read: EOPIE SUSPND TXD2IE RXD2IE TXD1IE 0 TXD0IE RXD0IE
Write:
UIR1 = $003A
USB Interrupt Register 1:
$003ARead: EOPF RSTF TXD2F RXD2F TXD1F RESUMF TXD0F RXD0F
Write:
UIR2 = $0018
USB Interrupt Register 1:
$0018Read: 00000000
Write: EOPFR RSTFR TXD2FR RXD2FR TDX1FR RESUMFR TXD0FR RXD0FR
UADDR = $0038
USB Interrupt Register 1:
$0018Read: USBEN UADD6 UADD5 UADD4 UADD3 UADD2 UADD1 UADD0
Write:
FLASH = $8000
I don't really get this. According to the docs, this is in the $0A00 - $ADFF range that is "Unimplemented"
VECTORS = $FFFE
This is the address of the Reset Vector
.area GSINIT0
Don't know what this means, just copied it from the sdcc generated assembly
entry::
I'm pretty sure double colons specify an exported entry point
ldhx #$0140
Load H:X from M H:X is the 2-byte "Index Register"
txs
Transfer H:X to SP So the previous $0140 becomes the value of the Stack Pointer. This is the end of RAM which goes from $0040 - $013F. This makes sense because the stack pointer decrements during pushes and increments during pulls.
mov #$80, UADDR
Sets the USBEN bit, enabling the USB module
mov #$3B, UIR0
Enable all Tx/Rx interrupts (TXD2IE | RXD2IE | TXD1IE | TXD0IE | RXD0IE)
mov #$FF, UIR2
Reset all flags
jsr __HC08Setup
Jump to Subroutine
jsr _main
done: bra done
Branch Always So, this is an endless loop for some reason
__HC08Setup:
mov #$01,MOR ; disable Watchdog
mov #$01,PPG ; select proper Clock Source for SCI
rts
;-----------------------------------------------------------------------------
; void initSCI();
;
_initSCI:: mov #$40,SCC1 ; Enable SCI
mov #$0c,SCC2 ; RE+TE
;
; Baudrate Calculation for 4.9152 MHz XTAL
;-----------------------------------------------
; BaudRate = ClockSource / (64 * Divisor)
; if ClockSource = BusClock = XTAL/4
; (set SCIBDSCR Bit in OPTION2!) then
; BaudRate = 4.9152 MHz / (4 * 64 * SCP * SCR)
; BaudRate = 19200 Baud / (SCP * SCR)
;-----------------------------------------------
; Rem: in Monitor Mode BusClock = XTAL/2!
;
mov #$00,SCBR ; 19200 Baud
rts
;-----------------------------------------------------------------------------
; putSCI(char c);
;
_putSCI:: brclr #7,*SCS1,_putSCI ; check SCTE flag
sta SCDR
rts
; char getSCI();
;
_getSCI:: brclr #5,*SCS1,_getSCI ; check SCRF flag
lda SCDR
rts
_putchar = _putSCI
_getchar = _getSCI
;-----------------------------------------------------------------------------
; void puts(char *s);
;
_puts:: psha
;
; load HX with integer argument from stack
;
ldx 4,sp
pshx
ldx 6,sp
pulh
;
putsloop: lda ,x
beq putsexit
jsr _putchar
aix #1
bra putsloop
putsexit: pula
rts
;-----------------------------------------------------------------------------
_main:: jsr _initSCI
;
clrh
clrx
delay1: aix #-1
cphx #0
bne delay1
;
mainloop: ldhx #message
pshx
pshh
jsr _puts
ais #2
jsr _getchar
bra mainloop
rts
;-----------------------------------------------------------------------------
message: .ascii "\r\n\r\n"
.ascii "HC08 Welcome Kit\r\n"
.ascii "http://elektronikladen.de/kit08.html\r\n"
.byte 0
;-----------------------------------------------------------------------------
.area memory(abs)
.org VECTORS
.word entry
;-----------------------------------------------------------------------------