# Why is there no DDR (data direction register) for PORTA on RCM4300?

**URL:** <https://forums.digi.com/t/why-is-there-no-ddr-data-direction-register-for-porta-on-rcm4300/19398>\
**Category:** Rabbit\
**Tags:** port\
**Created:** [April 17, 2018, 6:46am UTC](https://forums.digi.com/t/why-is-there-no-ddr-data-direction-register-for-porta-on-rcm4300/19398 "2018-04-17T06:46:25Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![rjames](https://avatars.discourse-cdn.com/v4/letter/r/a88e4f/32.png) [@rjames](https://forums.digi.com/u/rjames)\
**Post date:** [April 17, 2018, 6:46am UTC](https://forums.digi.com/t/why-is-there-no-ddr-data-direction-register-for-porta-on-rcm4300/19398/1 "2018-04-17T06:46:25Z")

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**Author:** ![TomCollins](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.digi.com/tomcollins/32/37_2.png) [@TomCollins](https://forums.digi.com/u/TomCollins)\
**Post date:** [April 17, 2018, 4:35pm UTC](https://forums.digi.com/t/why-is-there-no-ddr-data-direction-register-for-porta-on-rcm4300/19398/2 "2018-04-17T16:35:46Z")

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Port A is also used as the “slave port”. Bits 2-4 of SPCR control whether it’s all input, all output, a slave port or used for auxiliary I/O (an 8-bit data bus with a portion of port B used as address lines and a pin on port E used as a chip select).

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**Author:** ![rjames](https://avatars.discourse-cdn.com/v4/letter/r/a88e4f/32.png) [@rjames](https://forums.digi.com/u/rjames)\
**Post date:** [April 24, 2018, 11:18am UTC](https://forums.digi.com/t/why-is-there-no-ddr-data-direction-register-for-porta-on-rcm4300/19398/3 "2018-04-24T11:18:47Z")

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Thanks Tom. I do not find the digi documentation straight forward at all. It took me 2 days to find the SPCR reference. The 4300 documentation Section 5.2.1 Digital I/O is a couple of paragraphs with no mention of the 4000 uP documentation; very frustrating.