GAPMod comes in 3 variants:
- GAPMod1.x : bears a HyperBus Flash+RAM MCM
- GAPMod2.x : bears a Quad-SPI Flash and Quad-SPI RAM
- GAPMod3.x : mostly identical to GAPMod2.x, plus on-board 8-bit, low-cost STM8 MCU usable as system WatchDog/RTC/DeepSleep controller
HyperBus memory provides more bandwidth but is more expensive and possibly less easy to source than QSPI memories.

** File GAPMod_xxx_IO_Definition.xlsx documents the role of each GAPMod I/O and how they relate to GAP8 **


- Beware if switching from GAPMod1.2 to GAPMod2.x/3.x: 
  the level shifter that was present on UART signals in GAPMod1.2 is no longer present in GAPMod2.x.
  As a result, while UART signals were referenced to SAFE_VDD_IO at GAPMod1.2 boundary, they are
  referenced to SPIM_VDDIO (i.e. same as natively on GAP8) at GAPMod2.x/3.x boundary.
- There is a small number of differences between I/Os of GAPMod2.x and those of 3.x.
  Refer to file GAPMod_3.0_IO_Definition.xlsx.
  In particular, an always on 1.8V supply is required and replaces one of the couple of I/Os used to feed SPIM_VDDIO in GAPMod2.x.