Data Sheet

3. Functional Description

This chapter describes the modules and functions integrated in ESP32-WROOM-32D and ESP32-WROOM-

32U.

3.1 CPU and Internal Memory

ESP32-D0WD contains a dual-core Xtensa

32-bit LX6 MCU. The internal memory includes:

• 448 KB of ROM for booting and core functions.

• 520 KB of on-chip SRAM for data and instructions.

• 8 KB of SRAM in RTC, which is called RTC FAST Memory and can be used for data storage; it is accessed

by the main CPU during RTC Boot from the Deep-sleep mode.

• 8 KB of SRAM in RTC, which is called RTC SLOW Memory and can be accessed by the co-processor during

the Deep-sleep mode.

• 1 Kbit of eFuse: 256 bits are used for the system (MAC address and chip configuration) and the remaining

768 bits are reserved for customer applications, including flash-encryption and chip-ID.

3.2 External Flash and SRAM

ESP32 supports multiple external QSPI flash and SRAM chips. More details can be found in Chapter SPI in the

ESP32 Technical Reference Manual. ESP32 also supports hardware encryption/decryption based on AES to pro-

tect developers’ programs and data in flash.

ESP32 can access the external QSPI flash and SRAM through high-speed caches.

• The external flash can be mapped into CPU instruction memory space and read-only memory space simul-

taneously.

– When external flash is mapped into CPU instruction memory space, up to 11 MB + 248 KB can be

mapped at a time. Note that if more than 3 MB + 248 KB are mapped, cache performance will be

reduced due to speculative reads by the CPU.

– When external flash is mapped into read-only data memory space, up to 4 MB can be mapped at a

time. 8-bit, 16-bit and 32-bit reads are supported.

• External SRAM can be mapped into CPU data memory space. Up to 4 MB can be mapped at a time. 8-bit,

16-bit and 32-bit reads and writes are supported.

Both ESP32-WROOM-32D and ESP32-WROOM-32U integrate a 4 MB of external SPI flash. The integrated SPI

flash is connected to GPIO6, GPIO7, GPIO8, GPIO9, GPIO10 and GPIO11. These six pins cannot be used as

regular GPIOs.

3.3 Crystal Oscillators

The module uses a 40-MHz crystal oscillator.

Espressif Systems 6 ESP32-WROOM-32D & ESP32-WROOM-32U Datasheet V1.8