Alex-2-Graf/LENINGRAD-2-48k
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\# ROM Selection and Configuration Guide
> \[English](ROM.md) | \[Русский](ROM.ru.md)
The "Leningrad-2 2025 Revision" PCB provides flexible options for installing ROM chips. You can use standard vintage EPROMs or modern alternatives depending on your goals.
\## Supported ROM Chips
1\. \*\*Standard 48K Setup:\*\*
  \* \*\*2764 (К573РФ4/6)\*\* — Requires two separate chips. One holds the lower part of the ROM (Basic-48), and the other holds the upper part.
  \* \*\*27128 (К573РФ8)\*\* — A single chip that holds the entire 16 KB ZX Spectrum 48K ROM.
2\. \*\*Expanded Setup (with TR-DOS / BDI):\*\*
  \* \*\*27256\*\* — Allows you to store two different versions of TR-DOS or customized firmware.
  \* \*\*W27E256\*\* — A modern, electrically erasable (EEPROM) drop-in replacement for the 27256. Highly recommended for easy flashing.
\---
\## Jumper Settings for ROM
\* \*\*JP4 (ROM Type Selection):\*\*
  \* \*\*Short\*\* this jumper if you are installing \*\*two 2764\*\* chips.
  \* \*\*Leave Open\*\* if you are using a single \*\*27128\*\* or \*\*27256\*\* chip.
\* \*\*J12 (TR-DOS Firmware Selection):\*\*
  \* Active only when using a \*\*27256\*\* ROM. It switches between the two firmware banks stored on the chip.
\* \*\*JP5–JP9 (Memory Expansion Support):\*\*
  \* Must be soldered/shorted to ensure correct address lines routing for future memory expansions and multi-bank ROM configurations.

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# Video Configuration & RGB2VGA Setup
> [English](VGA.md) | [Русский](VGA.ru.md)
The Leningrad-2 2025 Revision features an integrated onboard **ZX_RGBI2VGA-HDMI** converter designed by AlexEkb. This converter uses a powerful Raspberry Pi **RP2040-Zero** board to upscale the vintage ZX Spectrum video signal to modern displays.
## Selecting Output: VGA vs. HDMI
The board can output video via either a standard VGA connector or an HDMI port.
### 1. HDMI Mode (Recommended)
* **Jumpers JP1, JP2, JP3:** Must be left **OPEN**.
* **Resistors R24 to R31:** You **MUST** replace the standard resistors with **270 Ohm** values to ensure proper signal voltage levels for HDMI stability.
### 2. VGA Mode
* **Jumpers JP1, JP2, JP3:** Must be **SHORTED**.
* Use standard resistor values as specified in the original schematic.
---
## Flashing the RP2040-Zero Firmware
To flash or update the video converter firmware via the onboard USB port, follow these crucial safety steps:
1. **Disconnect System Power:** Turn off the main power supply of the Leningrad-2 computer.
2. **Open Jumper J9:** Open/remove the **J9** jumper. *Crucial:* This completely isolates the RP2040-Zero power lines from the main computer board, preventing back-powering issues and potential hardware damage during flashing.
3. **Connect USB:** Connect a USB-C cable from your PC to the RP2040-Zero.
4. **Flash:** Hold the `BOOT` button on the RP2040-Zero, plug it in, and drop the `.uf2` firmware file onto the mounted drive.
5. **Restore:** Unplug the USB cable, **close/solder J9** back, and power on the computer.