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The HTL8254 is a synchronous implementation of the industry standard
8254/82C54 Programmable Interval Timer (PIT) adaptor. The PIT can be used
for a wide range of timing and counting functions.
The PIT provides three independently programmable 16-bits down-counters.
Each counter can be used for a number of timing task such as event counter,
elapse time counter, one-shot counter, baudrate generator, complex waveform
generator, square wave generator and many more.
The HTL8254 support 6 programmable counter modes, mode0: Interrupt on
Terminal Count, mode1: Hardware Retriggerable One-Shot, mode2: Rate
Generator, mode3: Square Wave mode, mode4: Software Triggered Mode and
mode5: Hardware Retriggerable Strobe.
Functional compatible with the industry standard PIT
6 Programmable counter modes
Status Read-Back command
Wide range of timing functions:
Prog. rate generator
Square Wave generator
Binary rate multiplier
Complex waveform generation
Complex motor control
Simple Processor/uController Interface
Binary and BCD counting options
No internal tri-state busses
Written in technology independent VHDL
Lowest cost commercial 8254 IP core
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Area and Performance
The table below shows a push button implementation of the standalone core for the 3 major FPGA vendors. The values given are
an indication of the required area and performance. No pin number, slewrate or I/O type was specified. Mentor Graphic's
Precision RTL 2007a.8 was used for synthesis.
The HTL8254 is delivered in synthesizable VHDL source code. The source code is fully documented and can be synthesized
using any modern synthesis tool. A partial self-checking VHDL testbench is included which verifies the 6 operating modes.
For evaluation the HTL8254 can be supplied on a low-cost FPGA development board from Enterpoint Ltd. The HTL8254 is
instantiated together with the HTL80186 processor, an HTL8259 Interrupt controller, an Opencores 16750 UART, a 146818
compatible Real Time Clock, an HTL8255 Parallel Port Interface and 40Kbyte of embedded SRAM. No VHDL source files will
be supplied in this case.