MC908AB32, ISP programmer - will it work?

cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 

MC908AB32, ISP programmer - will it work?

1,429 Views
bartek_zet
Contributor I
Hello.
I've build programmer shown on the picture. My question is: Will it work? Microcontroller will be supplied by 5V and Vtst  will be about 7,6V
Labels (1)
0 Kudos
1 Reply

211 Views
bigmac
Specialist III
Hello,
 
Welcome to the forum.
 
I can see a couple of potential problems with your schematic -
  1. For the standard MAX232 device, the capacitors C1, C2, C3 and C5 should have values of at
    least 1u0. 
    If you wish to retain the 100n values, you would need to use the MAX202 device
    instead.
  2. The source for Vtst should really be from the V+ pin, rather than T2out.  However, the use of
    the LM317 regulator is problematic.  Due to its significant drop-out voltage, and when
    supplied
    from the MAX232, it is unlikely that there would be suffient input voltage for the
    output to properly regulate to 8.0 volts.
Typically, there should be approximately 9 volts at the V+ pin, but this could vary, depending on the
serial port load.  Vtst should lie within the limits 7.5 to 8.0 volts (not a large margin for this particular
device).  Therefore, the regulator would need to be a low drop-out type.
 
As an alternative to using a regulator, you might connect two small signal diodes in series between
V+ and Vtst pins.
 
Regards,
Mac
 


Message Edited by bigmac on 2007-09-25 01:02 PM
0 Kudos