topic Re: HCS12XEP100/SPI. Is pull up on MISO necessary? in S12 / MagniV Microcontrollers

HCS12XEP100/SPI. Is pull up on MISO necessary?

AndersJ — Wed, 02 Feb 2011 19:03:33 GMT

It seems that the cpu has a internal pull up on the MISO.

Is this true?

If true:

* Is it safe to assume external pullup is not needed?

* Is this documented anywhere?

Anders J

Re: HCS12XEP100/SPI. Is pull up on MISO necessary?

kef — Wed, 02 Feb 2011 22:31:58 GMT

Which port is your MISO coming from? MISOs can found on ports P, M, S and H. Ports P and S have pullups enabled out of reset. M and H not. See corresponding pull device enable register description (PERP, PERM, PERS, PERH).

Table 1-10 summarises if and how each pin is pulled out of reset.

Re: HCS12XEP100/SPI. Is pull up on MISO necessary?

AndersJ — Thu, 03 Feb 2011 01:48:30 GMT

I did not realize that the pull ups enabled from reset stayed that way after setting up the port for SPI.

I incorrectly assumed that the setup available before configuring för SPI would be changed to "SPI-mode".

My first SPI uses port S, and seems to have a pullup, which you have now confirmed.

My second SPI is on port H, and has no pullup.

Is it a reasonably safe assumption that that pullups, drive capabilty and other configured port parameters

will remain unchanged regardless of which internal I/O module the port later is configured for?

Anders J