$DC07/56327/CIA1+7:   Timer B High-Byte (Tape, Serial Port)

   Read : Get current value

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

Kernal-Reference:

 ADC $DC07   : $F90B
 CPX $DC07   : $F935
 LDX $DC07   : $F92C
 STA $DC07   : $ED94 $EE22
 STX $DC07   : $FBB4
 STY $DC07   : $F940