NCO Glitch

[mpgmike]

I'm sending NCO values from one PIC to another. The Comm protocol requires 2 bytes per NCO1INCx register; 1st identifies it, 2nd is the NCO1INCx value. Finally there is a "Start" command byte sent. I noticed shooting for 2.4 MHz that I only got 564 Hz. However, if I turn the NCO Module Off, then On again, I get the 2.4 MHz. Here is the code for the Receiver:

DEFINE  OSC         8
DEFINE  HSER_RCSTA  90h             ;Enable serial port & continuous receive
DEFINE  HSER_TXSTA  02h             ;Disable transmit, BRGH = 0
DEFINE  HSER_CLROERR 1              ;Clear overflow automatically
DEFINE  HSER_BAUD   9600


;Configurations:
#CONFIG
    __config _CONFIG1, _FEXTOSC_OFF & _RSTOSC_HFINT32 & _CLKOUTEN_OFF & _CSWEN_OFF & _FCMEN_ON
    __config _CONFIG2, _MCLRE_OFF & _PWRTE_OFF & _WDTE_ON & _LPBOREN_OFF & _BOREN_ON & _BORV_LOW & _PPS1WAY_OFF & _STVREN_ON & _DEBUG_OFF
    __config _CONFIG3, _WRT_OFF & _LVP_OFF
    __config _CONFIG4, _CP_OFF & _CPD_OFF
#ENDCONFIG


;Aliases:
;Prb        VAR     LATA.0		       ;HF Generator Driver for Probes
;RX         VAR     PORTA.1		       ;USART Receive
;TX         VAR     PORTA.2		       ;USART Transmit
;MCLR       VAR     PORTA.3		       ;!MCLR
;NC         VAR     PORTA.4		       ;
;Wand       VAR     LATA.5 		       ;HF Generator Driver for IR LEDs


;Special Function Registers:
OSCCON1     =   %00000010                   ;INTTOSC, 1:4 Divider, 8 MHz
OSCFRQ      =   %00000011                   ;8 MHz
TRISA       =   %00001110
ANSELA      =   0
WPUA        =   0
    PPSLOCK = $55
    PPSLOCK = $AA
    PPSLOCK = 0                             ;Unlock PPS
;RA0PPS      =   %00011101                   ;Sets NCO Output to RA0, Pin 7
;RA5PPS      =   %00011101                   ;Sets NCO Output to RA5, Pin 2
RA2PPS  	=   %00010100                   ;Sets USART TX to RA2, Pin 5
RXPPS       =   %00000001                   ;Sets USART RX to RA1, Pin 6
    PPSLOCK = $55
    PPSLOCK = $AA
    PPSLOCK = 1                             ;Lock PPS
NCO1CON     =   %10000000
NCO1CLK     =   1                           ;NCO1 Clock = Fosc
PMD0        =   %01000101
PMD1        =   %00000101
PMD2        =   %01100110
PMD3        =   %01110011
PMD4        =   %00000000
PMD5        =   %00000111
VREGCON     =   3                           ;Lowest Power in SLEEP Mode
CPUDOZE     =   %10100100
INTCON      =   %01000000
TX1STA      =   %00000010                   ;$02
RC1STA      =   %10010000                   ;$90
BAUD1CON    =   %00000010
SP1BRGL     =   $0C                         ;Decimal 12, Yields 9600 BAUD
PIE1.5      =   1                           ;RCIE, USART Receive Flag


;Variables:
NcoL        VAR     BYTE BANK0 SYSTEM       ;USART NCO1INCL Value
NcoH        VAR     BYTE BANK0 SYSTEM       ;USART NCO1INCH Value
NcoU        VAR     BYTE BANK0 SYSTEM       ;USART NCO1INCU Value
Rec         VAR     BYTE BANK0 SYSTEM       ;USART Receive Register Value


;Constants:
Begin       CON     %10010000               ;USART Command to Start NCO, $90
Halt        CON     %10010001               ;USART Command to Stop NCO, $91
IR          CON     $92                     ;USART Command to Set NCO Output to LATA.5
Prb         CON     $93                     ;USART Command to Set NCO Output to LATA.0
NcoL_Val    CON     %10000001               ;USART Command, Following is NcoL, $81
NcoH_Val    CON     %10000010               ;USART Command, Following is NcoH, $82
NcoU_Val    CON     %10000011               ;USART Command, Following is NcoU, $83


;Labels:
Main:
    PIR1.5 = 0
    PAUSE 50
DO
    DO
        LOOP WHILE PIR1.5 = 0
    GOSUB Orders
LOOP


Run:
DO 
    IF PIR1.5 = 1 THEN
        GOSUB Orders
    ENDIF
    PAUSE 1
LOOP        


Slumber:
    NCO1CON.7 = 0
@   DOZE
@   NOP
GOTO Main
    
Orders:
    HSERIN [Rec]
;   Rec = RC1REG
    SELECT CASE Rec
        CASE IS = $81
            HSERIN [NcoL]
            NCO1INCL = NcoL
        CASE IS = $82
            HSERIN [NcoH]
            NCO1INCH = NcoH
        CASE IS = $83
            HSERIN [NcoU]
            NCO1INCU = NcoU
        CASE IS = $90
            STKPTR = STKPTR - 1
            PIR1.5 = 0
            NCO1CON.7 = 1.  ;Turn NCO On
            PAUSE 500
            NCO1CON.7 = 0. ;Turn NCO Off
            PAUSE 500
            NCO1CON.7 = 1. ;Turn NCO On
            GOTO Run
        CASE IS = $91
            STKPTR = STKPTR - 1
            PIR1.5 = 0
            GOTO Slumber
        CASE IS = $92
            PPSLOCK = $55
            PPSLOCK = $AA
            PPSLOCK = 0                             ;Unlock PPS
            RA5PPS  = %00011101                     ;Sets NCO Output to RA5, Pin 2
            PPSLOCK = $55
            PPSLOCK = $AA
            PPSLOCK = 1                             ;Lock PPS
            TRISA.0 = 1                             ;Shuts Down Alt Pin LATA.0
        CASE IS = $93
            PPSLOCK = $55
            PPSLOCK = $AA
            PPSLOCK = 0                             ;Unlock PPS
            RA0PPS  = %00011101                     ;Sets NCO Output to RA0, Pin 7
            PPSLOCK = $55
            PPSLOCK = $AA
            PPSLOCK = 1                             ;Lock PPS
            TRISA.5 = 1                             ;Shuts Down Alt Pin LATA.5
    END SELECT
    PIR1.5 = 0
RETURN

There is a slight delay in getting the 2.4 MHz output, which for this application is acceptable. Just wondering if I might have overlooked something simple.

[tumbleweed]

Swap the order you're writing to the registers... U, H, then L.

When the NCO module is enabled, the NCO1INCU and
NCO1INCH registers should be written first, then the
NCO1INCL register. Writing to the NCO1INCL register
initiates the increment buffer registers to be loaded
simultaneously on the second rising edge of the
NCO_clk signal.

The registers are readable and writable. The increment
registers are double-buffered to allow value changes to
be made without first disabling the NCO module.

When the NCO module is disabled, the increment
buffers are loaded immediately after a write to the
increment registers.

[mpgmike]

Thank you, I'll try that.

[mpgmike]

Thanks Tumbleweed! That did the trick. Reversed the order of the Send, removed the On-Off-On in the Receiver, get my correct output right out the gate.