BennVenn's analysis of Datel's Game Boy Modem indicated that the logo was stored in the MBC itself, and the MBC knows when to switch between the external ROM (for the desired logo) and the internal ROM (for the TMSS circumvention).Great Hierophant wrote:One curious thing however is that Rocket Games would display "ROCKET®", not "Nintendo®" on the bootup screen. The GBC checks some of these bytes to ensure that your ROM was displaying the correct name. Rocket Games presumably found a way to bypass the check, but when you replace the logo, the games work but now display Nintendo®.
Unfortunately, BennVenn's apparently taken down his old analysis pages.