Given that brick actually accepts rs232 and has an unlock compare string, its probably a z80 or 6809 or a similar 'true' cpu in there, with an eprom or mask rom. (Unlock: send the brick "p<NUL>###Do you byte, when I knock?$$$" and it responds "###Just a bit off the block!$$$" and unlocks itself. The much later Lego RCX 1.0/2.0 brick, which is Hitachi H8 based (and dumped), uses a nearly identical unlock phrase.)
"When life gives you zombies... *CHA-CHIK!* ...you make zombie-ade!"