To determine whether any of the unconnected pins of your chips require pull-up or pull-down resistors, we will need to refer to the datasheets of each component. Note that the datasheet excerpts provided don't directly specify the details of each pin regarding the necessity of pull-up or pull-down resistors.

In general, any input pins left unconnected may be susceptible to noise and could potentially settle at intermediate voltage levels causing increased power consumption or unintended behaviour. It is a common practice to attach pull-up or pull-down resistors to unconnected pins to avoid these issues[1].

The STM32F407ZET6 (U1) has internal pull-up and pull-down resistors that are designed with a true resistance in series with a switchable PMOS or NMOS[2]. However, the exact pins requiring pull-up or pull-down resistors aren't specified in the provided excerpts.

If we take the STM32F407ZET6 for example, pins like NRST (Pin 24), BOOT0 (Pin 137), and other I/O pins including PA0-PA15, PB0-PB15) typically have their pull-up and pull-down resistors configured according to the specific functionalities your design requires, as described in STM32F407ZET6 reference manual.

For IS62WV51216BLL-55TLI (U2), the datasheet excerpts provided don't specify which pins require pull-ups or pull-downs either. Generally speaking, for memory chips like this, the data pins (I/O0-I/O15 in the case of U2), address pins (A0-A18 for U2), and control pins (~CS1, ~WE, ~OE for U2) might need to have defined states and therefore might require pull-up or pull-down resistors.

Unfortunately, I couldn't provide an exact list of unconnected pins requiring pull-up or pull-down resistors without more datasheet information. It's recommended to refer to each component's respective datasheet or technical reference manual to decide whether a pull-up or pull-down resistor is necessary.

Remember to also consider your application, power consumption, noise immunity, and any potential states in your design where these pins might be left floating. These elements will help you to make the most appropriate decision when working with pull-up and/or pull-down resistors.

[1] Page 93

[2] Page 115

Sure, I'd recommend the CY62167EV30LL-45ZXI as a possible replacement for your current SRAM chip (IS62WV51216BLL-55TLI). This is a 4-Mbit (256K x 16) Static RAM chip from Cypress Semiconductor.

It has similar functionality with the following key characteristics:

Just like with any replacement, please ensure that it satisfies all your specific requirements and constraints before making the switch. The form, fit, and function should be checked in detail. You may also need to consider any potential certification issues that might arise due to component change.