[GPS_Standard] Custom PIC Chip to Regulate 20 MHz VCO

[Stanley Reynolds]

You would need to adjust the code as well.
Reduce the gate time from 16 sec to 8 sec would produce the same 6800 hex pulse count or change 6800 to D000 for 20 Mhz.
I have not considered the adjustments to the PC monitor program.
You may want to look at the 5 to 10 Mhz adjustments in the curent code:

ccp_160mhz_h                EQU 0x68                ;when frequency counted is exactly 160MHz, OLD_CCPR1 reads 26624, or 0x6800
ccp_160mhz_l                EQU 0x00                ; "
ccp_80mhz_h                 EQU 0xB4                ;when frequency counted is exactly 80MHz, OLD_CCPR1 reads 46080, or 0xB400
ccp_80mhz_l                 EQU 0x00                ; "
.
. <snip>
.
        BTFSS PORTB,bootup_freq_test                ;Is the frequency selection pin for 10MHz OCXO?
        BRA INIT_5MHz                               ;No, go initialize for 5MHz OCXO
INIT_10MHz                                          ;Yes, initialize for 10MHz OCXO
        MOVLW ccp_160mhz_h                          ;Load nominal value H to compare to measured frequency
        MOVWF NOMINAL_FREQ_VAL_H                    ; "
        MOVLW ccp_160mhz_l                          ;Load nominal value L to compare to measured frequency
        MOVWF NOMINAL_FREQ_VAL_L                    ; "
        BRA INIT_FREQ_COMPLETED                     ;Go continue initialization
INIT_5MHz                                           ;initialize for 5MHz OCXO
        MOVLW ccp_80mhz_h                           ;Load nominal value H to compare to measured frequency
        MOVWF NOMINAL_FREQ_VAL_H                    ; "
        MOVLW ccp_80mhz_l                           ;Load nominal value L to compare to measured frequency
        MOVWF NOMINAL_FREQ_VAL_L                    ; "

This would point to the pluse count method :

or 
ccp_320mhz_h              EQU 0xD0           ;when frequency counted is exactly 320MHz, OLD_CCPR1 reads 53248, or 0xD000
ccp_320Mhz_l                EQU 0x00
... 

INIT_20MHz                                          ;Yes, initialize for 20MHz OCXO
        MOVLW ccp_320mhz_h                          ;Load nominal value H to compare to measured frequency
        MOVWF NOMINAL_FREQ_VAL_H                    ; "
        MOVLW ccp_320mhz_l                          ;Load nominal value L to compare to measured frequency
        MOVWF NOMINAL_FREQ_VAL_L                    ; "
        BRA INIT_FREQ_COMPLETED                     ;Go continue initialization

If you wanted to force 20Mhz just use the code INIT_20MHz instead of the current code starting with BIFSS or better yet in place of the 5MHz case so the i/o pin would select 10 or 20 MHz.


Stanley

 
----- Original Message ----
From: Arie Dogterom <pa0ez at amsat.org>
To: gps_standard at mailman.qth.net
Sent: Tuesday, July 14, 2009 12:16:37 PM
Subject: Re: [GPS_Standard] GPS_Standard Digest, Vol 30, Issue 1

The chip will go to 50 MHz
Arie

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From: <gps_standard-request at mailman.qth.net>
To: <gps_standard at mailman.qth.net>
Sent: Tuesday, July 14, 2009 6:00 PM
Subject: GPS_Standard Digest, Vol 30, Issue 1


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>  1. Custom PIC Chip to Regulate 20 MHz VCO (P M Gant)
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> Message: 1
> Date: Tue, 14 Jul 2009 12:01:27 +0200
> From: P M Gant <ha5rxz at gmail.com>
> Subject: [GPS_Standard] Custom PIC Chip to Regulate 20 MHz VCO
> To: gps_standard at mailman.qth.net
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> <f2226b090907140301r14bd4f1avba0c7ee79b67e37f at mail.gmail.com>
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> Is it possible to prepare a custom version of the PIC to regulate a 20
> MHz oscillator or is this frequency too high?
> 
> HA5RXZ
> 
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