Hi,

I was wondering what other people have done in their designs to invoke the bootloader on the philips 89C51RD2. I'm designing a circuit that has an RD2 and a 128k SRAM chip. My -EA/VPP line is permantly tied to 5V. (i.e. always execute from internal ROM)

To invoke the bootloader I ground the
ALE/-PROG line and -PSEN line with a DPDT switch then press a push button to perform a ReSeT. So far this is what the ISP app note recommends.

I notice that the app note also says in 'uncertain' terms that 'we have found that it is necessary to tie P2.7 high' to invoke the bootloader. The app note needs to be rewritten to inspire more confidence in this area.

Should i also put P2.7 high via the switch, or do you think that the because of the connection to the SRAM chip, the line won't be pulled low and it will be pulled high because of the internal pull up in the RD2?