Abstract: An optional apparatus which can be connected to a printer or other optional apparatus includes a communication section for communicating with other apparatus and a control section which executes a command in response to the command received via the communication section; wherein the communication section has a first communication path for receiving a data string from an apparatus on the upstream side in communication and for transmitting the received data string to an apparatus on the downstream side of the communication and a second communication path for receiving a data string received from the apparatus on the downstream side of communication and for transmitting the received data string to the apparatus on the upstream side of the communication; and the control section executes a command in the command string received via the first communication path or the second communication path and loads the data indicating the execution result of the command in the command string.

Abstract: Programmers for an entry control system employ data carriers housing ROM chips. The ROM chips are affixed with unique elemental codes. A keypad addresses the chips in one-to-one correspondence with the keys to transmit the unique elemental codes to the programmable processor of the entry control system.