Hi,
did you update CPLD to the newest firmware? I think you has a older one. Firmware documentation and new firmware release was around June last year, see:
https://wiki.trenz-electronic.de/display/PD/TE0720+CPLD#TE0720CPLD-DocumentChangeHistory
PS:
QuoteAlso, I have asked this before, but does anyone know what device 0x21 is on I2C bus 1?
Are you sure that nobody answered?
https://forum.trenz-electronic.de/index.php/topic,1715.msg8128.html#msg8128
On older CPLD Version other I2C end device IP was used and 2 addresses was available, see a older obsolete documentation:
https://wiki.trenz-electronic.de/display/PD/TE0720+CPLD+archive+obsolete+description
br
John