M32C Port 9 DDR unlocking

John G 21 years ago

I am using the M32C/83 and bit banging I2C out on port 9. Port 9 requires the data direction register to be unlocked via PRCR before writing to PD9. Occasionally, PD9 isn't getting set and one of my I2C pins does not go low when it should. Bad things happen after that.

The H/W manual states that no interrupts or DMA should occur between the unlocking of PD9 and the writing of PD9. I lock out all maskable interrupts and ensure the unlock and PD9 access were contiguous.

Any suggestions or clarifications welcome.

(I'm thinking of reading back and verifying PD9 after I write to it and rewrite if necessary. Feels dirty...)

John G.

Vote

Enrico 21 years ago

Hi John,

I've been using the M16C for 4 years and the M32C/83 for two. I've never had problems with PD9 but I've never had to reconfigure the direction of PD9 at run time in a way that you are doing now, that is, continuosly. Therefore I can't be any help.

this might help!

ciao, Enrico

Vote

Peter Dickerson 21 years ago

is,

requires

PD9.

low

interrupts

I have used the M16C for bit banging I2C and I've also had to unlock PD9, though not for I2C but for key scan. It went something like this... (Mitsubishi compiler)

#if defined(KEYPORTDDR_NEEDS_UNLOCK) asm( " FCLR I"); PRCR = 4; // unlock DDR, not interruptable KEYPORTDDR = scan_table[1]; // enable interrupts asm( " FSET I"); #else KEYPORTDDR = scan_table[1]; #endif

where KEYPORTDDR was for port 9. I didn't have any DMA running.

So bit banging I2C on port 9 is likely to be slow because you'll need the unlock for every bit/clock. But you'll probably need the interrupt disable/enable anyway to stop port bit modifications from interfering - if they're messed with in interrupts.

Peter

Vote

John G 21 years ago

Thanks.

John G.

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required