# Why doesn't 9215 EXT\_WE# pulse when EXT\_CS0# pulses for a write?

**URL:** <https://forums.digi.com/t/why-doesnt-9215-ext-we-pulse-when-ext-cs0-pulses-for-a-write/22462>\
**Category:** NET+OS\
**Tags:** ext\_we, cs0-interface, 9215\
**Created:** [June 9, 2021, 9:13am UTC](https://forums.digi.com/t/why-doesnt-9215-ext-we-pulse-when-ext-cs0-pulses-for-a-write/22462 "2021-06-09T09:13:44Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![cjwilde](https://avatars.discourse-cdn.com/v4/letter/c/da6949/32.png) [@cjwilde](https://forums.digi.com/u/cjwilde)\
**Post date:** [June 9, 2021, 9:13am UTC](https://forums.digi.com/t/why-doesnt-9215-ext-we-pulse-when-ext-cs0-pulses-for-a-write/22462/1 "2021-06-09T09:13:44Z")

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We configured the 9215 to use CS0 as the inteface to an external device. We expect the EXT\_WE# and EXT\_OE# signals to work in conjunction with EXT\_CS0#, since we set BSP\_GPIO\_MUX\_CS0 to BSP\_GPIO\_MUX\_USE\_PRIMARY\_PATH.  
We scoped the EXT\_CS0# and EXT\_WE# signals. When we read/write the external device, we see the expected pulse on EXT\_CS0#. However, the EXT\_WE# signal does not pulse on a write. In fact, the EXT\_WE# signal shows a periodic waveform, with a 15ns low pulse every 16us.