# Is there 512KB battery backup external SRAM in RCM6750? **URL:** \ **Category:** Rabbit Software\ **Tags:** rcm6750, sram, rabbit\ **Created:** [February 26, 2015, 2:56pm UTC](https://forums.digi.com/t/is-there-512kb-battery-backup-external-sram-in-rcm6750/14440 "2015-02-26T14:56:28Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![maniac84](https://avatars.discourse-cdn.com/v4/letter/m/b4bc9f/32.png) [@maniac84](https://forums.digi.com/u/maniac84)\ **Post date:** [February 26, 2015, 2:56pm UTC](https://forums.digi.com/t/is-there-512kb-battery-backup-external-sram-in-rcm6750/14440/1 "2015-02-26T14:56:28Z")
Hi guys, Is there 512KB battery backup external SRAM in RCM6750? From the website - [http://www.digi.com/products/wireless-wired-embedded-solutions/solutions-on-module/rabbit-minicore/rcm6700#specs](http://www.digi.com/products/wireless-wired-embedded-solutions/solutions-on-module/rabbit-minicore/rcm6700#specs), it stated there is. But from the RCM6750 user manual ([http://ftp1.digi.com/support/documentation/90001191\_F.pdf](http://ftp1.digi.com/support/documentation/90001191_F.pdf)) on page 7, it does not state there is the battery backup external SRAM. ---
**Author:** ![petermcs](https://avatars.discourse-cdn.com/v4/letter/p/4af34b/32.png) [@petermcs](https://forums.digi.com/u/petermcs)\ **Post date:** [February 26, 2015, 4:01pm UTC](https://forums.digi.com/t/is-there-512kb-battery-backup-external-sram-in-rcm6750/14440/2 "2015-02-26T16:01:50Z")
Looking at the .org file when you compile one of the test programs with an RCM6750 as the target, I see an xmem3 section which is marked as bbram and is 1024K long. That seems conclusive proof that there is 1024K of external BBRAM (512K x 16 and not 512K x 8). Regards, Peter ---
**Author:** ![maniac84](https://avatars.discourse-cdn.com/v4/letter/m/b4bc9f/32.png) [@maniac84](https://forums.digi.com/u/maniac84)\ **Post date:** [February 26, 2015, 11:03pm UTC](https://forums.digi.com/t/is-there-512kb-battery-backup-external-sram-in-rcm6750/14440/3 "2015-02-26T23:03:30Z")
But from my RCM6750 .org file, the xmem3 does not marked as bbram. Only the bbrootdata, xmemdata, and fat\_buff has been marked as bbram. Total added up for bbrootdata, xmemdata, and fat\_buff is 8000h which is 32KB. I think this refers to the internal 32KB bbram. That’s why I’m wondering where is my external bbram goes? ---
**Author:** ![petermcs](https://avatars.discourse-cdn.com/v4/letter/p/4af34b/32.png) [@petermcs](https://forums.digi.com/u/petermcs)\ **Post date:** [February 27, 2015, 2:18am UTC](https://forums.digi.com/t/is-there-512kb-battery-backup-external-sram-in-rcm6750/14440/4 "2015-02-27T02:18:11Z")
that’s very strange. Which version of DC are you using? I tried it with 10.72. Also there is a note in the circuit diagram that says R30 is populated if fast RAM is fitted and R32 if low power RAM on the RCM7xx modules. Which is connected on your module. This determines whether the VCC or VBAT is connected to the RAM. ---
**Author:** ![maniac84](https://avatars.discourse-cdn.com/v4/letter/m/b4bc9f/32.png) [@maniac84](https://forums.digi.com/u/maniac84)\ **Post date:** [February 27, 2015, 8:17am UTC](https://forums.digi.com/t/is-there-512kb-battery-backup-external-sram-in-rcm6750/14440/5 "2015-02-27T08:17:56Z")
I’m still using the 10.66 version. Does it affect the .org file? ---
**Author:** ![petermcs](https://avatars.discourse-cdn.com/v4/letter/p/4af34b/32.png) [@petermcs](https://forums.digi.com/u/petermcs)\ **Post date:** [February 27, 2015, 8:40am UTC](https://forums.digi.com/t/is-there-512kb-battery-backup-external-sram-in-rcm6750/14440/6 "2015-02-27T08:40:46Z")
I’ve just done a quick comparison with 10.66 and 10.72 for the Samples\RCM6700\SWITCHLEDS.C program and it does indeed make a difference. 10.66 shows xmem3 as normal RAM, 10.72 shows it as BBRAM. Looks like there was a change made in 10.70 or 10.72. Update: It was in 10.70 according to the release notes: [http://ftp1.digi.com/support/sampleapplications/40002719\_F.txt](http://ftp1.digi.com/support/sampleapplications/40002719_F.txt)