#ALTERA QUARTUS II V.9.0 LICENSENO CODE#
#ALTERA QUARTUS II V.9.0 LICENSENO PC#

#ALTERA QUARTUS II V.9.0 LICENSENO PC#

The data at the first PC location is decoded by the Op-code decode block which in turn controls the sequencing of the control unit.

#ALTERA QUARTUS II V.9.0 LICENSENO CODE#

If you instantiate a memory block configured as single port ROM and point the initial file to the assembled binary file, then each time you modify the processor code, all you have to do it compile the FPGA and the new code will automatically be included in the compile. The assembler can create either of these, although I use MIF files. Altera has two memory file formats, HEX and MIF. Program memory is internal to the FPGA РІР‚вЂњ typical code size might be just 1 kB, which can be implemented in two Altera memory blocks (each block is 512Р“вЂ”9 bits). Then it starts addressing the program memory at address $0000 (the Fetch cycle).

It was simpler to just allow sufficient time for the memory data to be read or written.Р”Р„t startup, the internal state machines are reset and the program counter (PC) is cleared. The reason I use more than one cycle for each element is the structure of the Altera FPGA memories, which must be registered for the address (or is the data? it is one of them, or possibly both). There are four elements to each instruction cycle: Fetch, Decode, Execute, and Write-Back. This may seem to be an excessive amount of time РІР‚вЂњ and it is РІР‚вЂњ but it did make for a simple internal state machine.

When programming, you need to be aware of this restriction, as there are no assembler warnings if you exceed this number.Р”В®ach instruction cycle takes a fixed 16 clocks, so at 27 MHz (the clock I usually use for the PT13) each instruction takes about 600 ns. To implement subroutine branches, three registers form a FIFO to hold the program counter contents, allowing a maximum of three nested routines. This means events have to be polled, which is a little wasteful of power, but as the code is relatively simple, and given the savings it allows РІР‚вЂњ for example, not needing to keep a copy of all the registers РІР‚вЂњ it was a worthwhile compromise. To keep a minimal footprint for the processor, I decided to forgo interrupts. I also stripped out the two 16-bit stack pointer registers. I decided to strip out the 16-bit registers from the 6809, although I kept a limited indexing operation using Accumulator B because it is handy for referencing tables. Р”Р‡igure 1 The PT13 homebrew microprocessor block diagram The block diagram of the processor, which I call the PT13, is shown in Figure 1. I loosely based the design on my favourite, the 6809, but soon started stripping it bare, finally managing to squeeze a workable processor into less than 400 logic elements (LEs РІР‚вЂњ basically a 4-input look-up table followed by a programmable flip-flop РІР‚вЂњ the building blocks of FPGAs), allowing it to fit in the smallest of FPGAs, or allow multiple instantiations in the same FPGA. I decided to design my own minimal microprocessor for those simple tasks such as I 2 C control of peripherals, or simple control interfaces such as digital encoders and character LCD displays. Although FPGA-based processors were available, such as AlteraРІР‚в„ўs Nios, they did use quite of lot of resources and often required external code memory, encumbered as they were by C compilers and even operating systems. I used FPGAs a lot in my designs and usually needed a processor for some housekeeping or control purpose. I was thinking of designing it into an FPGA РІР‚вЂњ just for fun РІР‚вЂњ when a more pressing need took hold. My own favourite processor was the Motorola 6809 and I used it as a workhorse in my early days as an engineer, using an old Dragon home computer as a development tool. I enjoy reading the articles of those eccentric engineers emulating past microprocessors such as the 68000 or even a Cray. This article is about one such diversion.

But you do get to spend a few days exploring some dimly lit avenue of electronics without having marketing asking you to produce yet another PowerPoint presentation for management that tries to justify their inspired idea that breaks a fundamental law of physics. Freedom? Well, of a sort РІР‚вЂњ you do still need to produce things that might sell. That could have been me, but when Personnel departments became Orwellian Human Resource departments producing dictates banning you from taking leave during Team Building Days, I decided to leave employment and start my own company. Do you see that grumpy old engineer in the corner of the lab who delights in sending new graduates down to stores to get a bag of holes.

Altera quartus ii v.9.0 licenseno