elekterminal bell - grabs your attention

grabs your attention One of the great things about com- puters is that no matter what you tell them to do they never complain and always stay quiet. Sometimes, however, it is helpful if a computer can make some noise to catch your attention. In the KB-9 BASIC or Junior BASIC the ASCII character 07 is an "end of line" indicator, and represents "BELL (control + G on the keyboard). The extended Junior does not use this signal, but it can if the circuit shown here is built. The circuit diagram shows just how simple the hardware for this "bell" is. When the ASCII character 07 (0000 0111) appears on lines BO . . . B6 (the data output lines of the UART on the Elekterminal) and the DAV (data available, UART pin 19) line is high (indicating that the whole character has been re- ceived) the output of NAND gate N5 goes "low". This signal then goes to the TRIGGER input of monostable multivibrator IC3. The external timing components connected to pins 1, 2 and 3 of this 4047B determine the widt...