In: A=Envelope number (1..15), HL=Pointer to Data (must be >3FFFh)
The data block starts with a header byte:
bit7 envelope type (0=software, 1=hardware) bit6 repeat flag (0=one shot, 1=repeat envelope) bit6bit5-0 number of following 3-byte parameters (1..5)
The following 3-byte parameters can be (when Byte 0 is <F0h):
Byte 0 Number of steps (01h..EFh)