PCJR BIOS: Really?

[ChildOfCv]

I've been taking a close look at PCJR's cassette BASIC, just for the fun of it. But I'm wondering if the ROM dumps out there that I found are accurate. Does anyone here have a PCJR? And if so, could you run debug.exe and type:

 

d f600:1b90 l 10

 

I see the following in the ROM images, but this is clearly wrong, as it means that any USR call from cassette BASIC (that is, no cartridge BASIC and no disk in the drive on boot) will crash the system.

 

F600:1B90 87 DE 56 8B 17 81 FA FF FF 03 E9 BC F4 0E BB 07

 

But I'm still curious, maybe there are some data integrity issues in the BIOS?

 

As a comparison, the PC BIOS looks like this:

 

F600:1B90 87 DE 56 8B 17 80 FA FF 75 03 E9 BC F4 0E BB 07

 

which has its own bug: If the USR address is set to x*256-1 for any integer x, then it will result in an "Illegal function call" error.