{"id":5423,"date":"2023-07-12T16:36:47","date_gmt":"2023-07-12T14:36:47","guid":{"rendered":"http:\/\/www.retro.co.za\/blog\/?p=5423"},"modified":"2024-12-29T14:59:26","modified_gmt":"2024-12-29T12:59:26","slug":"cmac-r2133-20-48mhz-tcvcxo","status":"publish","type":"post","link":"http:\/\/www.retro.co.za\/blog\/?p=5423","title":{"rendered":"CMAC R2133 20.48MHz TCVCXO"},"content":{"rendered":"<p><a href=\"http:\/\/www.retro.co.za\/blog\/wp-content\/uploads\/2023\/07\/R2133.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-5424\" src=\"http:\/\/www.retro.co.za\/blog\/wp-content\/uploads\/2023\/07\/R2133.jpg\" alt=\"\" width=\"705\" height=\"727\" \/><\/a><\/p>\n<p>I have two PCBs from a piece of defunct Nortel equipment with this oscillator. CMAC R2133 Freq 20.48 MHz. Looking at the circuitry around it, there&#8217;s a 16-bit DAC (AD7846), a 5V regulator (78L05) and a buffer (74F00). Google could not find me a datasheet, so I removed the oscillator to trace the pinouts (Nortel used the outside layers as groundplane, you will see nearly every trace goes from a component to a via. Makes it difficult).<\/p>\n<p>Pin 1 is 0V, pin 2 is the output, pin 3 is 5V, and pin 16 is the control voltage from the DAC which is configured to supply 0-5V out via the 51R1 resistor R40 and a 47u capacitor C77. The output goes to pin 2 of the 74F00 via 33R2 R53.<\/p>\n<p>I posted the above pic <a href=\"https:\/\/www.facebook.com\/groups\/ElectronicParts\/permalink\/2216031605252829\/\">to Facebook<\/a>, within an hour or two someone sent me the datasheet (well, the Nortel spec sheet, which is basically the datasheet in reverse). It is indeed a TCVCXO, pinouts as I&#8217;d already determined (pins 4-15 are N\/C), giving -10 to -15 ppm with 0V on the control pin and +10 to +15 ppm with 4V on the control pin.<\/p>\n<p>Stick this thing through an 11 stage binary counter and you get 10 kHz, <a href=\"https:\/\/www.qsl.net\/zl1bpu\/MICRO\/SIMPLE\/SimpleGPS.htm\">add a PIC and a GPS<\/a> and it could be the most accurate thing on your bench.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>I have two PCBs from a piece of defunct Nortel equipment with this oscillator. CMAC R2133 Freq 20.48 MHz. Looking at the circuitry around it, there&#8217;s a 16-bit DAC (AD7846), a 5V regulator (78L05) and a buffer (74F00). Google could not find me a datasheet, so I removed the oscillator to trace the pinouts (Nortel used the outside layers as groundplane, you will see nearly every trace goes from a component to a via. Makes it difficult). Pin 1 is 0V, pin 2 is the output, pin 3 is 5V, and pin 16 is the control voltage from the DAC&#46;&#46;&#46;<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[75,117],"tags":[],"class_list":["post-5423","post","type-post","status-publish","format-standard","hentry","category-electronics","category-reverse-engineering"],"_links":{"self":[{"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5423","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5423"}],"version-history":[{"count":6,"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5423\/revisions"}],"predecessor-version":[{"id":5809,"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5423\/revisions\/5809"}],"wp:attachment":[{"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5423"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5423"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5423"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}