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iUP-200A/201A
Fuse Protection:
Firmware Development
Microprocessors and microcomputers are central elements in designing electronic
products. The typical developm ent process for m icroprocessor- and
microcomputer-based systems involves integrating hardware and software. Once
the software is perfected, it is often installed permanently in a read only memory
(ROM) device. Software installed in ROM is referred to as firmware. Firmware is
used in systems design because of its relative low cost, high speed, and data non
volatility. Non-volatility means that firmware is retained even when system power
is turned off.
Intel manufactures a wide variety of ROM memory components which can be
divided into two general types: masked ROMs and electrically programmable
ROMs (PROMs).
Intel fabricates firmware into a masked ROM during manufacturing. This is often
the most cost effective method for including firmware in a mass-produced product.
Programs and data are electrically programmed into a PROM. To electrically pro
gram a PROM, data is presented to a particular address. Voltage is then applied to
programming pins to set (burn in) the code in the selected cell.
Bipolar PROMs can be electrically programmed only once; thereafter, they retain
their data permanently. The programs or data programmed into an EPROM can be
erased by exposing the device to ultraviolet light. An E2 PROM can be electrically
erased in a manner similar to that used to program it.
EPROMs and E2 PROMs allow flexibility during firmware development because
they can be erased and reprogrammed. Some microcomputer components, such as
the Intel 8751, have built-in EPROMs in addition to other logic.
For design convenience, some microcomputer components have pin-compatible
counterparts containing masked ROM instead of EPROM. This allows the re
programmable EPROM version to be used during prototype development and the
masked ROM version to be used for the final mass production.
PROM Programming Overview
All PROMs have a characteristic physical word length. This word length is the
number of parallel bits that are accessed when a given address is specified. Almost
all of Intel's recent PROM components have an 8-bit word; however, many earlier
PROMs had 4-bit words.
The difference between a PROM's physical word length and the logical word
length used in a system must be considered when programming the PROM. For
example, two 8-bit PROM devices must be connected in parallel to provide the 16-
bit-wide memory word that the 8086 microprocessor requires. To put an 8086 ma
chine language program (consisting of a series of 16-bit words) into 8-bit PROM
devices, the machine code must be formatted so that the 16-bit words are mapped
correctly into each pair of 8-bit devices. For example, the first PROM might be
programmed with the upper eight bits of each machine code word, while the
second PROM might be programmed with the lower eight bits of each machine
code word.
100 VAC, use 2 ampere slow blow
120 VAC, use 2 ampere slow blow
220 VAC, use 1 ampere slow blow
240 VAC, use 1 ampere slow blow
General Information
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