On Reset the BOS rom is activated.
Bits 7 and 6 written to FBBD are ignored. Bit 5 is for enabling the ram expansion. Bit 2,1,0 set the bank.
Bit 3 is documented as enabling and disabling the ROM, but I found it didn't work exactly like that.
If bit 3 is set to 1, and upper ROM is enabled with port 7fxx, then ROM on the Vortex RAM Expansion is enabled in the range &c000-&7fff.
If bit 3 is set to 1, and lower ROM is enabled with port 7fxx, then ROM on the Vortex RAM expansion is enabled in the range &c000-&7fff.
If bit 3 is 0, then normal operation happens. ROM is visible in the range &c000-&7fff only if ROM slot 6 is selected and the upper rom is enabled with port 7fxx. When bit 3 is 0, the rom is not visible in the range &0000-&3fff at any time.
It is possible this part of my (arnoldemu) vortex ram expansion is broken, but all other operation works perfectly and the BOS rom is active at reset time and can be used as normal.
== Description ==