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Low-cost single chip clock monitor circuit

Published on Aug 03 2010 // Single Chip Microcomputer circuits


Low-cost single chip clock monitor circuit

1 . Overview: Here, we design a low-cost single chip HT48R05A clock display circuit , using a combination display unit that displays four 7-segment digital , such as display ” hours: minutes “or” minutes : seconds “value , also set the four buttons to use At calibration time , Sui Ran General SCM Mei You Shiyongbiaozhun school when special crystal , time Yebu easy to do Feichangzhunque ( for example, required no more than a month Wucha 1s), The time control circuit still has a lot of Application space. By extension , any other series of MCU resources to achieve basic enough , such EM78P153 so , but their instructions are not necessarily the same, but the programming is basically the same. We use HT48R05A-1 of PA0-PA6 mouth as the mouth section of line (because only 7 , PA7 not ) , the output section of digital data , and other spare port ( depending on PCB layout and convenient, with any five I / O port May be ) as a bit driver output , because the circuit we used a NPN transistor as the driver tube , then the digital control must be a common cathode , of course, can also use the common anode , but the need to use PNP drive transistor , and the program is just the bit operation The opposite.

We use four digital tube (LED) display units display dynamic scanning , PA mouth line also has had four keyboards were used as controls ( such as ” hours, minutes , seconds , ” the set , “Start” , “Select “” Power ” button , etc. ) . PA output port to another for both the input port , the procedure must always change its port -line , as output , you must write to its control register “0” , and as an input port line, to its control register write “1 . ” Therefore, the working state of PA is always changing , dynamic scanning required scan frequency can not be too low , otherwise the figures will show flashing , the general frequency of not less than 50Hz, not feel flash , this procedure is relatively easy to implement. Program we use the timer interrupt to implement the time plus or minus , then the main program only need to monitor the dynamic scan output and keyboard . In the timer interrupt process of the hours, minutes or seconds plus ( or minus the time ) operation , and update data sent to the display buffer , so when the time dynamic scanning display unit can be taken from the display buffer . This design we used HT48R05A-1 almost all of the resources , to achieve ” best use ” purposes , in order to enable the lowest cost, the price has a strong competitive advantage , of course HT48R05A-1 of the ROM capacity of only 512Byte, but For just as the time display is fully adequate , as long as a reasonable arrangement process , the program is not complicated.