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~Here Larry helps teach us a little bit more about this Code
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EPROM sizes and
types
EPROMs come in several
sizes both in physical packaging as well and storage capacity. While parts
of the same type number from different manufacturers are compatible as long
as they're only being read, there are subtle differences in the programming
process.
Most EPROMS could be identified by the programmer through
"signature mode" by forcing 12V on pin A9 and reading out two
bytes of data. However, as this was not universal, programmer software also
would allow manual setting of the manufacturer and device type of the chip
to ensure proper programming.[8]
eproms – wikipedia
The
following information may have errors; It is not permissible to be read by
anyone who has ever met a lawyer. Use is confined to Engineers with more
than 370 course hours of electronic engineering for theoretical studiesve errors; It is not permissible to be read by
anyone who has ever met a lawyer. Use is confined to Engineers with more
than 370 course hours of electronic engineering for theoretical studies
EPROM Size
Rating
EPROMs are rated in k-bits where k is equal to
1,024 and the EPROM number generally (but not always) reflects the size.
But when we talk about memory size, we speak in terms of k-bytes. To
change bits to bytes, simply divide the number of bits by 8 to get bytes. A
couple of examples will clear things up: The 2716 EPROM number ends in 16
and thus is 16 k-bits in size or 16 * 1,024 or 16,384 bits. Now, 16,384
bits divided by 8 gives us 2,048 bytes or 2 k-bytes. Thus a 2716 is a 16
k-bit EPROM, but is most often expressed as being 2 k-bytes in size. Some
EPROMs are word wide or 16 bits (2 bytes) wide. These EPROMs are also rated
in bits, such as 27C1024 ; a 1 M-bit
(Mega-bit), 1,024 k-bits, 128 k-bytes, or 64 k-word EPROM. Such EPROMs come
in 40 pin packages to allow for the extra pins needed.
EPROM(Erasable Programmable
Read Only Memory) can be programmed and erased
enabling them to be re-used. Erasure is accomplished using an UV (Ultra
Violet) light source that shines through a quartz erasing window
in the EPROM package. There also are OTP (One Time
Programmable) EPROMs, sometimes called OTPROMs (One Time
Programmable Read Only Memory),
that are identical to an erasable EPROM, but lack an erasing window
to reduce costs. To reduce the cost, these EPROMs come in a windowless
plastic carrier, which is cheaper than the costly ceramic package
required for the erasing window. They can be programmed one time only, so
these are used after the code is bug free.
All EPROM bits are set to a 1 when erased (each byte = FFh). When programming an EPROM you can only change the
1s to 0s or clear bits. If you program a byte to 10100101 (A5h), only the
0s locations change state. Once a bit is changed to 0, you can't change it
back to a 1 without erasing the whole EPROM. We can go back and change any
of the 1s to 0s in a second programming session called patching. For example,
the A5h byte (10100101) can be changed to 21h (00100001) but it can not be changed to F5h (11110101). Once more,
remember programming clears bits, but only erasing the EPROM sets them.
Programming an EPROM requires a special program voltage
called Vpp (25, 21 or 12.5 Volts). Parts that use
a Vpp of 12.5 also require us to raise the Vcc from 5v to 6v during programming
Once the programming voltage is applied, we apply the
address location and data to be programmed into the EPROM. The data comes
from an EPROM image in a memory buffer This Image is loaded from another
EPROM or disk file. Then using one of the programming algorithms, we apply
a programming pulse. The best deal in programmers is the pocket programmer.
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