A simple USB emulated serial interface provides for control/readout of the TDC. The output is C5 code described in the IEEE paper, with encoding as given in Table I. 'Q0 codes are sent continuously when the link is idle. Other codes may be sent by using the commands below.

The input logic expects 8B/10B data in serial format at 25Mb/s. A 'K.28.1 code synchronizes the link and starts a transmission. Then 2048 words of 32 bits are received and stored in a block RAM for readout.

The emulated serial port operates at 9600 baud, 1 stop bit, no parity and no handshaking. When the board is powered up, after a 1s delay the message:

  TRM1.0
  >

is sent and the board waits for text commands terminated by a CR or LF. All characters sent from the computer are echoed for convenience in operating with a terminal program.

After any output from the command, a new >' prompt is sent. Commands are documented ​here (Google document)