74ALS74 DATASHEET PDF

EAB3 skin Register. Today's Posts Search. Diagram PCB and components. Franchute13 29 September I'll rewrite everything to help someone else in the future.

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Compared to the first version this version features updated MMU with four banks, each one of those banks can be mapped to any 16 KiB page in 1 MiB on-board memory. The FDC is replaced with 37C For interrupts to function properly Z80 needs to be set to interrupt mode 2.

JP1 is a software configuration jumper. It can be read by software using RTC port 70h bit 6. Note that pin 1 is the pin that is closer to the parallel connector.

Warning: If JP2 is set incorrectly, it is possible to create a short circuit of the 5 Volt power supply. P4 is the parallel port connector. Many components have multiple part numbers listed in BOM.

There are some differences between various part numbers, such as:. If unsure what to order, read specifications on seller's and manufacturer's web sites. Also please read Replacement Notes below. Finally, consult people on N8VEM news group.

Make sure that the tip of the power supply is the positive lead. Also floppy disk drives are relatively power hungry about 1 A max. Jameco carries quite a few regulated switching 5V wall adapters with different amperage.

See these catalog pages:. Alternatively it is possible to use a linear power supply with or similar voltage regulator make sure to use a heatsink, especially if powering a floppy drive.

Page select registers are used to map physical memory pages to the banks in Z80 address space:. That page should contain a boot loader that among other things configures and enables memory paging. The content of page select registers is unknown after a power on or a reboot.

These registers need to be initialized before enabling memory paging. During the initialization the page select register for bank 0 needs to be set to page 0. So that CPU continues to execute instructions from that page.

The page select registers are implemented as 8-bit registers. Only 7 lower bits are decoded by Zeta SBC V2 memory chip select logic, and only 6 lower bits are actually used to address the memory. Output to the channel 0. Configure the channel in the counter mode. Set the time constant to Output to the channel 1.

Configure the channel in the counter mode and enable interrupt when counter reaches 0. Set bits of the interrupt vector. Bits are set to the value of I register, bits 2 and 1 are set to the CTC channel number that caused the interrupt. Bit 0 is always 0. Note that each interrupt vector takes 2 bytes of memory and it should start on an even address. Output L to the selected channel.

This configures the channel in the counter mode with interrupts enabled. Output to the selected channel. This sets bits of the interrupt vector. Bits are set to the I register, bits 2 and 1 are set to the CTC channel number that caused the interrupt.

Real Time Clock. It uses a CR battery for power backup. The DS has a 3-wire serial interface, and it is programmed through the RTC register 70h using bit-banging. It is normally used for connecting a console or terminal. Use a null modem cable to connect to a PC. It uses PC compatible pinout. This signal is ignored by most all? Connector P6 - 5V P6 is the 5V power output for the floppy drive.

Alternatively it can be used instead of P1 for supplying power to the board. It is recommended to use a polarized header for P6 to avoid incorrect power polarity which probably will destroy FDD or components on the SBC board. Please pay attention when upgrading from older boards.

The polarity marking on the silkscreen is correct. Obviously I didn't order all of components listed here, and I was not able to actually verify that they will work. Please make sure to double check specifications on manufacturer's and seller's web site before ordering. Please let me know if you found any problems or incompatibilities. There are some differences between various part numbers, such as: Different manufacturer.

For example Texas Instruments vs. National Semiconductor for IC. For some other components, for example connectors, sockets, or capacitors, it could be some difference in the quality. Mechanical differences, especially for switches. Pick whatever suits best in your enclosure.

Some other minor differences. For example: RoHS or Pb-free vs. Price differences For some reason some components are priced much higher than other otherwise similar parts. Some eBay sellers ask premium price for components because of their perceived uniqueness keywords: vintage, rare, NOS, collectible , or special packaging e.

It is too long for some floppy disk drives you'll notice that standoff doesn't go completely inside the floppy drive mount hole. In this case cut a few millimeters using a file or a fine saw. This will reduce the power consumption. You might want to select the switch according your own preferences, for example the enclosure type you want to use, and whatever you want the reset button to stick out of the enclosure or to stay hidden inside.

Works on frequency up to 20MHz. It is possible to use MAX or other parts that need 1uF capacitors. In this case capacitors C21 - C24 have to be replaced with 1uF capacitors. Pay attention to capacitors' polarity if using electrolytic capacitors. Oscillators It is possible to use half can oscillators instead of full can oscillators.

In this case install oscillator at pins 4 - Refer to the PCB silkscreen for oscillator placement. Mods Mods described here were intentionally not implemented on PCB to keep it simple. If you don't plan to use PPI, it can be omitted. It is possible to build Zeta SBC V2 without floppy disk controller for example for the test purposes, or if you don't need floppy.

Board rerouted, most of ICs moved around or shifted. It already supports the full image programming Add incorrect power supply polarity protection Option 1: Schottky diode in series Option 2: Diode connected in parallel to power supply, in reverse could be dangerous if power supply is not short circuit protected Option 3: Use FET. Uses only through hole components. Assumes using commonly available 3. Although it should work with 5. Only 2 configuration jumpers.

PCB mounted connectors, no need to build cables. Hardware Documentation File downloads are at the bottom of this page. Make sure that memory page select registers are configured properly before enabling paging.

Programming Notes The content of page select registers is unknown after a power on or a reboot. Channels 0 and 1 are chained together. This port is used as the interrupt output in PPI modes 1 and 2. The CTC clock is connected to the trigger input of channel 0, and the ZC zero count output of channel 0 is connected the trigger input of channel 1. So that channel 0 will divide the clock, and the resulting signal will be divided further using channel 1.

In this example channel 0 is programmed with time constant of , so it will divide the input clock by , resulting in 3. The channel 1 is programmed with down counter of , and will divide 3.

That channel is also programmed to generate an interrupt every time counter reaches 0. In this case a CTC channel needs to be programmed for counter mode operation with time constant of 1. Jumper Position. P4 pin 25 is connected to the ground.

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74ALS74 Datasheet

Latest Projects Education. JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding. Thread starter kelumsd Start date Nov 14, Search Forums New Posts. Thread Starter kelumsd Joined Nov 14, Unfortunately I couldn't find that IC within my area.

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