Available online
Description
This programme examines the role and composition of the interface that links the CPU with the computer's peripherals.
This programme examines the role and composition of the interface that links the CPU with the computer's peripherals.
| Module code and title: | TM221, The digital computer |
|---|---|
| Item code: | TM221; 07 |
| First transmission date: | 21-06-1975 |
| Published: | 1975 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:23:33 |
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| Producer: | Ted Smith |
| Contributors: | Roger Loxton; Steve Matheson |
| Publisher: | BBC Open University |
| Keyword(s): | CPU/peripheral communication; Digital computing; Lighting board; Minicomputer system; Output interface; Translation sequence |
| Footage description: | The opening sequence illustrates the use of an interpreter in a telephone conversation between an English salesman and his French client. Roger Loxton uses this as an analogy of the role of the computer's interface in linking the CPU with the computer's peripherals. Steve Matheson further develops this analogy of input-output programming. He uses graphics to demonstrate the relationship between the CPU, the output interface and the output peripheral. In particular he explains the composition of such links as the I/O bus. Using a large illuminated graphics board representing the hardware structure of the output interface, Matheson describes the functions of the major components of this interface. He explains the way in which the following works the device selector; the function selector; the buffer; the buffered flag. Matheson now explains in detail how the interface operates as a complete system during I/O operations. Continuing to use the graphics board, he explains how the computer sends a character for printing through the interface, and what part each component on the interface plays. Loxton examines the actual PDP-8 computer's instructions which send the signals to the interface. He explains how they operate and illustrates his points with a chart. Further use of the telephone link analogy, showing the difficulty of interrupting the person at the other end of the line when using a translator. Matheson shows how a similar problem can occur in a computer. He explains how the interrupt facility works in the hardware of the PDP-8 computer's interface. Uses illuminated graphics throughout. Loxton explains the software changes necessary to introduce an interrupt facility into the PDP-8 program. He uses a chart to show these alterations in detail. Matheson reviews the achievements of the program so far. Loxton then introduces to the viewer aspects of the studio's PDP-8 computer. He runs a program for paper tape output, and then operates the interrupt routine in its simplest form. Loxton next explains the advantages of a more efficient use of the interrupt facility, whereby it does not affect paper tape output. The demonstration of this routine on the PDP-8 concludes the programme. |
| Master spool number: | 6HT/71775 |
| Production number: | 00525_5167 |
| Videofinder number: | 1465 |
| Available to public: | no |
