CRTC hardware differences

Hardware differences

There are several slightly different versions of the 6845. The BBC series require a 6845S varient as the VDU drivers depend on certain functionality:

• R3 Vertical Sync.
• R6 Vertical Displayed any odd/even value, to set to 25 in MODE 3,6,7.
• R8 Character Delay and Cursor Delay timing for MODE 7.