# Why is a 16 pin header suggested for use with SwitchBlox Rugged, which has an 18 pin stacking header? **URL:** \ **Category:** BotBlox Hardware\ **Tags:** switchblox-rugged\ **Created:** [December 17, 2024, 12:55pm UTC](https://forum.botblox.org/t/why-is-a-16-pin-header-suggested-for-use-with-switchblox-rugged-which-has-an-18-pin-stacking-header/359 "2024-12-17T12:55:04Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![botblox\_admin](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.botblox.org/botblox_admin/32/1_2.png) [@botblox\_admin](https://forum.botblox.org/u/botblox_admin)\ **Post date:** [December 17, 2024, 12:55pm UTC](https://forum.botblox.org/t/why-is-a-16-pin-header-suggested-for-use-with-switchblox-rugged-which-has-an-18-pin-stacking-header/359/1 "2024-12-17T12:55:05Z")
In the SwitchBlox Rugged the pin header suggested for stacking two boards is 16 positions while the stacking header on SwitchBlox is 18 positions. Is this correct? ---
**Author:** ![josh\_elijah](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.botblox.org/josh_elijah/32/568_2.png) [@josh\_elijah](https://forum.botblox.org/u/josh_elijah)\ **Post date:** [December 17, 2024, 12:56pm UTC](https://forum.botblox.org/t/why-is-a-16-pin-header-suggested-for-use-with-switchblox-rugged-which-has-an-18-pin-stacking-header/359/2 "2024-12-17T12:56:08Z")
There is an 18 pin header on SwitchBlox Rugged revision F, but the pin header is only 16 pins. This is because there are two positions to plug in the pin header for SwitchBlox Rugged (left-side oriented and right-side oriented). This is described in the datasheet. ![image](https://canada1.discourse-cdn.com/flex027/uploads/botblox1/original/1X/47ed132e7aee35304ef0e7e7ac4c16fdae7a5abc.png) We did this because it was a smart way either connect the management interface between two boards or not. For SwitchBlox Rugged back-to-back applications, you don’t want the management bus to be shared between both boards, and using a 16 pin header allows us to skip two pins. ---
**Author:** ![botblox\_admin](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.botblox.org/botblox_admin/32/1_2.png) [@botblox\_admin](https://forum.botblox.org/u/botblox_admin)\ **Post date:** [October 7, 2026, 5:24pm UTC](https://forum.botblox.org/t/why-is-a-16-pin-header-suggested-for-use-with-switchblox-rugged-which-has-an-18-pin-stacking-header/359/3 "2026-10-07T17:24:35Z")
Anonymized customer question, shared by BotBlox for reference. We are connecting two SwitchBlox Rugged Rev F boards (BB-SWR-F-1) back-to-back to form a 10-port switch, following section 2.2.4 of the October 2023 datasheet. The datasheet specifies a left-justified 16-position M22-2520805 header so that the I2C\_SDA / I2C\_SCL connections are not connected between the boards. Since the second board is mirrored, a header on J2 pins 3–18 of Board 1 appears to occupy pins 1–16 of Board 2. This puts Board 2’s I2C pins 1/2 onto Board 1’s pins 17/18, which are unlabeled in Figure 8. 1. Which J2 pins should be connected or left unconnected on each board? 2. What signals do pins 17 and 18 carry? 3. Is the specified 16-position header correct, or is a 14-position header needed to leave pins 1/2 open on both boards? 4. What is the complete board-to-board pin mapping? ---
**Author:** ![botblox\_admin](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.botblox.org/botblox_admin/32/1_2.png) [@botblox\_admin](https://forum.botblox.org/u/botblox_admin)\ **Post date:** [October 7, 2026, 5:25pm UTC](https://forum.botblox.org/t/why-is-a-16-pin-header-suggested-for-use-with-switchblox-rugged-which-has-an-18-pin-stacking-header/359/4 "2026-10-07T17:25:30Z")
BotBlox reply: That mapping is correct. On SwitchBlox Rugged Rev F (BB-SWR-F-1), J2 pins 17 and 18 are NC: they have no electrical connection to the board circuitry. Figure 8 leaves these contacts unlabeled, which makes the assembly instructions unclear. The specified 16-position M22-2520805 header is correct. Taking Board 1 as the board where the header occupies J2 pins 3–18: - Board 1: pins 1/2 are physically unoccupied. - Board 2: pins 17/18 are physically unoccupied. - Board 2’s I2C pins 1/2 mate with Board 1’s NC contacts 17/18. The two boards’ I2C buses therefore remain electrically isolated. Here is the complete connection list, using each board’s own J2 numbering: Board 1 ↔ Board 2 - 3 GTXCTL ↔ 15 GRXCTL - 4 GTXCLK ↔ 16 GRXCLK - 5 GTXD0 ↔ 13 GRXD0 - 6 GTXD1 ↔ 14 GRXD1 - 7 GTXD2 ↔ 11 GRXD2 - 8 GTXD3 ↔ 12 GRXD3 - 9 VIN ↔ 9 VIN - 10 GNDREF ↔ 10 GNDREF - 11 GRXD2 ↔ 7 GTXD2 - 12 GRXD3 ↔ 8 GTXD3 - 13 GRXD0 ↔ 5 GTXD0 - 14 GRXD1 ↔ 6 GTXD1 - 15 GRXCTL ↔ 3 GTXCTL - 16 GRXCLK ↔ 4 GTXCLK - 17 NC ↔ 1 I2C\_SDA - 18 NC ↔ 2 I2C\_SCL A shorter 14-position header is not needed. Assemble the boards with power disconnected and in the back-to-back orientation shown in Figure 9 of the [October 2023 datasheet](https://store-l0hv1zrcre.mybigcommerce.com/content/SwitchBlox%20Rugged%20Rev%20F%20DataSheet%20%28Oct%202023%29.pdf#page=13). The VIN and ground connections are shared through J2. Josh ---
**Author:** ![botblox\_admin](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.botblox.org/botblox_admin/32/1_2.png) [@botblox\_admin](https://forum.botblox.org/u/botblox_admin)\ **Post date:** [October 7, 2026, 5:26pm UTC](https://forum.botblox.org/t/why-is-a-16-pin-header-suggested-for-use-with-switchblox-rugged-which-has-an-18-pin-stacking-header/359/5 "2026-10-07T17:26:34Z")
Anonymized customer follow-up: The pin mapping is clear. Since both boards are identical, can either physical board be Board 1 (header on J2 pins 3–18), provided the assembly follows the Figure 9 orientation and pin mapping, and operate as a single unmanaged 10-port switch? Does applying external power to one board determine which board must be Board 1, when the other board is powered through J2 (VIN/GNDREF)? ---
**Author:** ![botblox\_admin](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.botblox.org/botblox_admin/32/1_2.png) [@botblox\_admin](https://forum.botblox.org/u/botblox_admin)\ **Post date:** [October 7, 2026, 5:27pm UTC](https://forum.botblox.org/t/why-is-a-16-pin-header-suggested-for-use-with-switchblox-rugged-which-has-an-18-pin-stacking-header/359/6 "2026-10-07T17:27:31Z")
BotBlox reply: Yes, both SwitchBlox Rugged boards are identical. “Board 1” and “Board 2” are just labels in the assembly diagram, rather than different board types or roles. As long as you follow the back-to-back orientation and J2 pin mapping above, either physical board can go in either position. The power rail is electrically shared through J2, so it doesn’t matter which board you connect the power supply to. One supply powers both boards. Josh