some food for testing
Send in mode 6 download and execute.
ldaa #YY 86 YY
staa byte_fc 97 fc
ldy xxxx 18 ce XX XX
ldx off_ffb0 fe ff b0 update fix
jsr 0,x ad 00 fix
rtn 39
YY=length of reply message
XXXX= start address to dump data.
We can also set it: when you upload a data, the pcm will write and than read the written data and reply back with the data stored. Something like an echo message.