Cnc machining nm09/2
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- 4.10 Computer hardware
- 4.10.1 Input devices
- 4.10.2 Central processing unit (CPU)
- 4.10.4 Output devices
- 4.11 Punched tape
- 4.11.1 What the columns mean
- 4.11.2 Tape material
- 4.11.3 Tape terminology
4.9 Review of computer terms
Figure 4.14 Desk top computer system The subject of computers generally focuses on two broad aspects, computer hardware and computer software 4.10 Computer hardwareThe term computer hardware is a general term used to describe the computer and the peripheral devices which aid in the use of the unit. These devices are often considered under the following headings:
4.10.1 Input devicesAs the name implies, input devices are used to enter data into the computer. Among the more common of such devices are:
4.10.2 Central processing unit (CPU)The central processing unit (CPU) is the computers centre of activity. This is made up of electronics circuits that interpret and execute program instruction and communicates with the input, output and storage devices. 4.10.3 Storage devicesBecause RAM (Random Access Memory) is only a temporary method of storing data, more permanent storage methods must be used to save NC data. This can be done by:
4.10.4 Output devicesOnce the CPU has processed the data some form of output is requires. This output can be in the form of man readable information or coded signals which only decoding devices can interpret. More common output devices include:
4.11 Punched tapePunched paper tape and tape punchers were among the first input/output devices to be used with computer. Compared with printing speeds today, they are somewhat slow —with tape readers operating at speeds of 300 to 1000 characters a second, and tape punchers at speeds slower than that. The slow reading and punching speeds, poor durability and the difficulty of adding or deleting data has led to punched tape being gradually superseded by other technology. The sketch below shows a typical tape reader. 
Figure 4.15 tape reader 4.11.1 What the columns meanEach column of holes on the tape either represents a numerical value or has some special meaning. The sketch shown below describes what each of these eight columns means. The columns are numbered from right to left, which follows the standards and also the binary coded system on which the standard is based. 
Figure 4.16 4.11.2 Tape materialWhile the maximum thickness and other dimensions of punch tape has been standardised, the materials from which tape is made has not. The four types in general use are:
4.11.3 Tape terminologyThe following terminology applies to punched tape used in programming. A character. Any number, letter or symbol which can be seen on the keyboard of a type writer or computer is referred to as a character. Some characters such as G and M are very commonly used while others such as % or / are special characters having meanings specific to a particular MCU. Row. A row is a path of holes perpendicular to the edge of the tape where the holes for one character are located. Channel. A channel is a path parallel to the edge of the tape, that can contain a hole or no hole, depending on the characters. There are eight channels on the tape used. Sprocket. The sprocket is the smaller hole or channel between channels three and four and is used to propel the tape through the reader and for timing control within the CNC system. Word. A word is a combination of characters that represent an axis command, a sequence number, or a function. The first character in each word must be a latter address. For example: N49 X13 Y001 M05. The first word is the sequence number (N49), the next two words are axis commands, (X123 Y001) while the last word (M05) is a miscellaneous function command. Block. A block is a combination of words that represents one complete sequence of commands. The block length is variable, since the blocks need to contain only those command words that have changed from the previous block. If only one axis or only one function is changed from the previous block, the new block only needs to have the words which have changed from the preceding block. For example: N50 G01 X25 Y50 M03 N51 X50 N52 Y40 M09 Parity. The term parity refers to a system used to identify and proofread punch tapes which have been produced under the EIA or ACSIIIISO standards. EIA standard. Tapes cut under the EIA standards have what is referred to as ‘odd number parity’. Put simply this means that each character is represented as an odd number of holes across the tape. The example below shows the odd number parity format for the EIA standard codes. 
Figure 4.18 EIA ASCII/ISO standard. To distinguish between this and the EIA standard ASCIIIISO tapes have even number parity. The example below shows the even number parity format of ASCIIIISO standard codes. 
Figure 4.19 ISO/ACCII Directory: file -> view view -> Western Europe after wwii view -> Author study: paul fleischman view -> Qpa1 7ela study Guide view -> Arctic Oil/Gas Neg view -> November 1970 Approximately 150,000-500,000 deaths Bhola Cyclone Bangladesh view -> Grade Level: 6 Unit of Study: Caribbean glce view -> Citation: Duffield, Katy view -> Table of Contents Lesson # view -> Chinese Wind Energy Disad Download 0.53 Mb. Share with your friends:
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