Getting BASIC3 to work


I'm trying to get BASIC3 working on my ELF MAX. I have the MCSMP20.bin file loaded into ROM at 8000H. If I enter C0 80 00 at 000H and run it, I get the MCSMP prompt and the commands work fine. I've used the M,W,S,L,T,R,V and H commands at 9600 baud using a USB console cable and TeraTerm. When I issue the B command, I get the BASIC3 startup message and the C/W? prompt. I type 'C' and it says ready and gives me the ':' prompt. So far, so good. If I type in 'PR "HELLO"' it prints HELLO. But if I enter 'PR MEM', it says "-.32E+08" instead of the roughly 32K I would expect. When I try to enter a line of code like '10 PRINT "HELLO"', I get the message "". Has anyone else seen this, or know what that warning means? How does BASIC3 determine how much memory is available?