What is an octal buffer and how is it used in electronic circuits?

[iggybaseball]

Hello, I am new to electronics and have been reading as much as I can about the subject when time permits. I am doing a project to make an adapter to hook a ttl magnetic swipe reader to my computer via the gaming port. There are also plans to make an adapter that would allow you to connect it to the parrallel port. One of the components of the parrallel adapter is an octal buffer. I do not understand what this component does. Anyone?

 

[Ouabache]

A buffer is temporary storage component (like RAM), where data is gated n-bits at a time. A good example using the parallel port, is the printer. The printer is slower at printing than the electronic flow of bits (hi and low signals) through the parallel port. This is especially true for pixel intensive images. So the buffer holds the data until the printer has finished its operation on the last group of data, then gates in some more.

Octal refers to base-8 numbering system. This can be represented in binary numbers using 3-bits. (0 to 7, represented by 000 to 111).

Looking at the specs for an http://www.semiconductors.philips.com/acrobat_download/datasheets/74F540_541_2.pdf (base-16, represented by 0 to F), which is very common for computer apps, you can represent them in binary from 0000=0 to 1111=F. You can input any number in hex (0 to F) using 4-bits and an octal buffer can accept two 4-bit inputs. (To represent a single octal number, you would only need 3 input lines).

 

[chroot]

Ouabache is incorrect. The term buffer does not refer to a memory component at all, in hardware -- perhaps Ouabache confused a buffer with a register?

A buffer (like the one Ouabache linked to) is simply a unity-gain amplifier, usually with a very high input impedance and a very low output impedance. It allows a designer to connect a source which cannot tolerate being heavily loaded (i.e. cannot produce a lot of current without changing its voltage) to another load which requires a lot of current (e.g. a capacitive load). It is used to "isolate" one device from another by eliminating loading effects. It provides a "buffer" between the two devices.

The term 'octal,' of course, simply means eight, since there are eight independent amplifiers in the chip.

- Warren

 

[iggybaseball]

Thanks a lot guys.

 

[Ouabache]

Buffers are commonly used between a computer and an external device (like a printer) as I mentioned. My description of a buffer is correct, just not for your application. Upon further reflection (and good night’s sleep), I also recalled another use of the term buffer, as in buffer-amplifier with the desirable characteristics that chroot pointed out.

It makes sense in this context, octal is referring to eight amplifiers on this chip. To test this hypothesis, I compared an octal to a http://www.semiconductors.philips.com/acrobat_download/datasheets/74HC_HCT367_CNV_2.pdf . If you follow my link you will find there are only six amplifiers on it.

Typical magnetic stripe readers only require 4 lines, so a hex-buffer would work just as well in that case. Also to avoid having to build a separate power supply for 5v, you may want to stay with the (DB15) game port which already has that supply available.

[It is amazing where our minds may lead, when half asleep]