Bloader on 16F88

Support for Bloader and Screamer

Moderator: phalanx

Post Reply
njcnjc
Posts: 1
Joined: Sat Nov 08, 2008 5:24 pm

Bloader on 16F88

Post by njcnjc » Sat Nov 08, 2008 5:31 pm

Hi,

I've programmed a 16F88 with Bloader. I am having trouble using Screamer to load a program onto it.

I have a USB-to-Serial cable that I hacked up from an old cell phone cable. There are 3 output pins from this cable: GND, A, B.
A has 3.25V to GND and B has 0V. When I open Hyperterminal and use a very low Baud rate, type something in, the voltage on A drops momentarily. From this I determined that A = TX and B = RX.

I have the following setup on the 16F88:


Vss (Pin 5): Ground
Vdd (Pin 14): +5V

RX (Pin 8 ): A from USB-to-Serial
TX (Pin 11): B from USB-to-Serial

Nothing else is hooked to the microcontroller.


I am thinking that perhaps the 3.25V on the USB-to-Serial is a little bit too low for communicating with the 16F88. Any ideas?

jasonharper
Support Volunteer
Posts: 845
Joined: Wed Mar 02, 2005 12:14 pm
Location: Oklahoma
Contact:

Post by jasonharper » Sat Nov 08, 2008 6:22 pm

3.25V is a bit on the low side for the serial input - you need 80% of Vdd to guarantee a logic '1'. The 16F88 is rated for operation down to 4 volts, you could try temporarily reducing the supply voltage (perhaps by putting a diode or two in series with the +5V supply) when programming.

Re: "Nothing else is hooked to the microcontroller" - I hope you at least have a bypass capacitor across the power supply pins!

riden
Support Volunteer
Posts: 1754
Joined: Fri Jun 03, 2005 10:41 pm
Location: Illinois

Post by riden » Sat Nov 08, 2008 9:47 pm

jasonharper wrote:Re: "Nothing else is hooked to the microcontroller" - I hope you at least have a bypass capacitor across the power supply pins!
And a 10k or so pull up on the MCLR line as well.

When you first program the 16F88 Screamer bootloader, when you reset the device, it will look for a handshake from the PC and then enter a loop that prints "Ok" to the terminal. You should be seeing that.
Ralph

Post Reply