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EDN Access--06.19.97 µC-based one-shot has wide range

-June 19, 1997



June 19, 1997

µC-based one-shot has wide range
Yongping Xia, International Teldata Corp, Los Angeles, CA

The µC-based, digitally programmable, monostable multivibrator in Figure 1 has more accurate timing than a conventional RC-based device because a 20-MHz crystal controls the µC. The PIC16C54 is a low-cost, high-speed, 18-pin µC. At a full speed of 20-MHz and using the accompanying program, this µC can generate programmable pulses of 10 µsec to 100 sec per step. (Click here to download the file from DI-SIG, #2050.)

Inputs S0 through S6 control the step size (Table 1), and S7 through S9 determine the range (Table 2). When S7=S8=S9=logic 0, S0 through S6 determine the pulse width, which can range from 10 µsec to 1.27 msec with 10 µsec per step. When S7=S8=S9=logic 1, each step is equivalent to 100 sec. Thus, the maximum pulse width is 3 hours, 31 minutes, and 40 sec. (DI #2050)

Figure 1

 

A µC- and crystal-based monostable multivibrator exhibits much more accurate timing than its RC-based counterpart.
Table 1--Timing step sizes (when S7=S8=S9=0)
S6 S5 S4 S3 S2 S1 S0 Time (msec)
0 0 0 0 0 0 1 0.01
0 0 0 0 0 1 0 0.02
      .        
      .        
      .        
1 1 0 0 1 0 0 1.00
      .        
      .        
      .        
1 1 1 1 1 1 0 1.26
1 1 1 1 1 1 1 1.27
Table 2--Range-control settings
S9 S8 S7 Factor (x)
0 0 0 1
0 0 1 10
0 1 0 100
0 1 1 1000
1 0 0 10,000
1 0 1 100,000
1 1 0 1 million
1 1 1 10 million


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Copyright c 1997 EDN Magazine, EDN Access. EDN is a registered trademark of Reed Properties Inc, used under license. EDN is published by Cahners Publishing Company, a unit of Reed Elsevier Inc.

 

 

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