;-----------------------------------------------------------------------------
; cryosc.ASM
;-----------------------------------------------------------------------------
; Copyright 2001, Cygnal Integrated Products, Inc.
;
; FILE:        cryosc.ASM
; DEVICE:      C8051F02x
; ASSEMBLER:   Keil A51
; AUTH:        BW
; DATE:        23 JUL 01
;
; This program provides an example of how to configure the C8051F02x device
; to operate from an external 22.1184MHz crystal attached to the XTAL1 and
; XTAL2 pins.  Also enables Missing Clock Detector.
;
;-----------------------------------------------------------------------------

;-----------------------------------------------------------------------------
; EQUATES
;-----------------------------------------------------------------------------

$INCLUDE (C8051F020.inc)

LED         EQU      P1.6        ; LED on target board ('1' is LED ON)

SYSCLK      EQU      22118       ; SYSCLK frequency in kHz

;-----------------------------------------------------------------------------
; VARIABLES
;-----------------------------------------------------------------------------

;-------------------
; STACK

STACK       SEGMENT IDATA        ; declare STACK segment
            RSEG  STACK
            DS    80h            ; reserve 128 bytes for stack

;-----------------------------------------------------------------------------
; MACRO DEFINITIONS
;-----------------------------------------------------------------------------

;-----------------------------------------------------------------------------
; RESET AND INTERRUPT VECTOR TABLE
;-----------------------------------------------------------------------------

            CSEG AT 0
            ljmp  Main                    ; RESET vector

;-----------------------------------------------------------------------------
; MAIN PROGRAM CODE
;-----------------------------------------------------------------------------

CRYOSC      SEGMENT  CODE                 ; declare CODE segment
            RSEG  CRYOSC                  ; select CODE segment
            USING 0                       ; using register bank 0

Main:
            mov   WDTCN, #0deh            ; disable watchdog timer
            mov   WDTCN, #0adh

            mov   SP, #STACK-1            ; init stack pointer

            mov   OSCXCN, #67h            ; enable external crystal
                                          ; oscillator at 22.1184MHz

            clr   A                       ; wait at least 1ms 
            djnz  acc, $                  ;  wait ~512us
            djnz  acc, $                  ;  wait ~512us

osc_wait:                                 ; poll for XTLVLD-->1
            mov   a, OSCXCN
            jnb   acc.7, osc_wait

            orl   OSCICN, #08h            ; select external oscillator as 
                                          ; system clock source
            orl   OSCXCN, #80h            ; enable missing clock detector

            sjmp  $                       ; spin forever

;-----------------------------------------------------------------------------
; End of file.

END