RP235x is Raspberry Pi's new MCU product family that provides both security and I/O flexibility in the low-cost MCU domain through selectable dual ISA cores at boot time (Arm Cortex-M33 or RISC-V Hazard3), ARM TrustZone and OTP-based Secure Boot, and 12 PIO state machines and HSTX. This white paper describes the product lineup, processor and memory and bus architecture, boot ROM, power and clock, peripherals, and development ecosystem based on design decisions and tradeoffs from the INSEM webinar presentation slides and technical Q&A, while also specifying application boundaries such as lack of USB High Speed support and inability to use PSRAM for XIP.