$DC06/56326/CIA1+6:   Timer B Low-Byte (Tape, Serial Port)

   Read : Get current value

   Write: Set Low-Byte of value to count down from

Kernal-Reference:

 LDA $DC06   : $F8FE
 SBC $DC06   : $F932
 STA $DC06   : $FBB1
 STY $DC06   : $F93D