To proceed with completing the connection of the rest of the pins, we need to establish the function of the project. Here, we're dealing with a Z80 CPU (U1), an ESP32 devkit (U2), and an AT28C64B EEPROM (U3). One common utilization scenario could be using the ESP32 to upload programs to the Z80 through the EEPROM. If that's the case, we'll have to set up the connection appropriately.

Making the assumption that you want to keep the GPIOs of ESP32 as flexible as possible, I recommend using some GPIOs for connecting to the control pins of Z80 and EEPROM to operate them properly like controlling program read/write.

Let's see how we can connect various control and data lines.

For Z80 CPU (U1), Here are the additional connections you might need to make:

For EEPROM (U3):

Remember, these are just suggestions. It would be better to follow specific interfacing requirements from Z80 and ESP32 documentation and your application requirements.

Also, if any connections mentioned above conflict with the existing Nets in your project, please do rearrange these as per your convenience and requirement.

ESP32 is there only to generate clock signal to clock pin on z80

Ah, I see. If the ESP32 is only there to generate the clock signal for the Z80, then most of its pins can be left unconnected. You've already connected the ~CLK~ pin of the Z80 (U1) to the D13 pin of the ESP32 (U2), which is good for generating the clock signal.

The Z80 CPU (U1) and EEPROM (U3) connections seem to be complete for a basic operation where the Z80 would fetch instructions from the EEPROM. The address lines (A0 through A12) and data lines (D0 through D7) are properly connected between U1 and U3.

Nonetheless, there are some control signals that need to be addressed for both U1 and U3. For instance:

Remember to check the specific datasheets of the components to see the effect of these signals and how they should be handled when not in use, as some signals can be left unconnected, others must be tied to VCC or GND.

Plus, you might need some additional components (e.g. decoupling capacitors near the power supply pins) to assure stability. Please account for them in your design.

what about memory request on the z80?

The ~MREQ~ (Memory Request) line is an active low control signal output by the Z80 (U1) to indicate when it's trying to perform a read or write operation with memory (as opposed to an I/O device).

If the Z80 is only interacting with the EEPROM (U3) as its memory, there is no need for additional connections. However, if there were additional memory or peripheral devices, you would use ~MREQ~ in combination with ~RD~ or ~WR~ to orchestrate read or write operations.

You can consider connecting the ~MREQ~ line from the Z80 (U1) to the ~CE (Chip Enable) line of the EEPROM (U3). This coupling can help manage the enabling of the chip. When ~MREQ~ is active (low), it indicates that a memory-related operation is being requested, so the EEPROM can be enabled (making ~CE line low).

Let's state it more formally:

Before you perform this step, make sure to study the datasheets of your components carefully to ensure that these operations are compatible with your memory modules and overall system design.

Based on the provided schematic connections, I can see that both memory and data address pins of the components are already connected, as well as power and ground. If you're looking to use more functionalities from your components, here are some suggestions:

ESP32-DEVKIT-V1 (U2) You can consider using the IO pins (D2, D4, D5, D15, D18, D19, D21, D22, D23, D25, D26, D27, D32, D33, D34, D35, RX2, TX2) for peripherals and there are possibilities for implementing communication protocols like SPI, I2C, or UART if needed[1].

However, note that you need to take care to avoid the strapping pins (EN, VP, and VN) at power-on because these pins are used to determine the boot mode of the module. These pins must be at certain logic levels upon startup.

Also, remember that some pins are dedicated to flash/PSRAM communication and should not be used for other purposes.

Z80 CPU (U1) For the Z80, there are some control signals that might be useful depending on your application:

AT28C64B-15PU (U3) For the EEPROM you might want to consider connecting the pin WE to activate the write enable[2].

Some of your ESP32 DEVKIT V1 are still disconnected. However, before proceeding to the connection of the extra pins, you need to clarify the functionality you want to add to your design, as the pins should be connected according to the desired functionality.

[1] Page 17

[2] Page 2