Input-Output Configuration
The terminal sends and receives serial information. Each quantity of information has 8 bits of an alphanumeric code. The serial information from the keyboard is shifted into the input register INPR. The serial information for the printer is stored in the output register OUTR. These two registers communicate with a communication interface serially and with the AC in parallel. The input—output configuration is shown in figure. The transmitter interface receives serial information from the keyboard and transmits it to INPR. The receiver interface receives information from OUTR and sends it to the printer serially.
Fig: Input-Output Configuration
Scenario1: when a key is struck in the keyboard, an 8-bit alphanumeric code is shifted into INPR and the input flag FGI is set to 1. As long as the flag is set, the information in INPR cannot be changed by striking another key. The control checks the flag bit, if 1, contents of INPR is transferred in parallel to AC and FGI is cleared to 0. Once the flag is cleared, new information can be shifted into INPR by striking another key.
Scenario2: OUTR works similarly but the direction of information flow is reversed. Initially FGO is set to 1. The computer checks the flag bit; if it is 1, the information is transferred in parallel to OUTR and FGO is cleared to 0. The output device accepts the coded information, prints the corresponding character and when operation is completed, it sets FGO to 1.
No comments:
Post a Comment