User's Manual

ESP-32S User Manual
Shenzhen Ai-Thinker Technology Co., Ltd http://www.ai-thinker.com
3. Functional Description
This chapter describes the modules and functions integrated in ESP-32S.
3.1 CPU and Internal Memory
ESP32-DOWDQ6 contains two low-power Xtensa® 32-bit LX6 microprocessors. The internal memory
includes:
•
448 KB of ROM for booting and core functions.
• 520 KB of on-chip SRAM for data and instruction.
• 8KB of SRAM in RTC, which is called RTC SLOW Memory and can be accessed by the co-processor during
the Deep-sleep mode.
•
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.
• 1 kbit of eFuse, of which 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-DOWDQ6 supports up to four 16-MB external QSPI flash and SRAM with hardware encryption based
on AES to protect developer’s programs and data.
ESP32 can access the external QSPI flash and SRAM through high-speed caches.
• Up to 16 MB of external flash are memory-mapped onto the CPU code space, supporting 8, 16 and
32-bit access. Code execution is supported.
• Up to 8 MB of external flash/SRAM are memory-mapped onto the CPU data space, supporting 8, 16 and
32-bit access. Data-read is supported on the flash and SRAM. Data-write is supported on the SRAM.
ESP-32S integrates 4 MB of external SPI flash. The 4-MB SPI flash can be memory-mapped onto the CPU code
space, supporting 8, 16 and 32-bit access. Code execution is supported. The integrated SPI flash is connected
to GPIO6, GPIO7, GPIO8, GPIO9, GPIO10 and GPIO11. These six pins cannot be used as regular GPIO.
3.3 Crystal Oscillators
The frequencies of the main crystal oscillator supported include 40 MHz, 26 MHz and 24 MHz. The accuracy
of crystal oscillators applied should be ±10PPM,and the operating temperature ranges from-40°C to 85°C.
When using the downloading tools, remember to select the right crystal oscillator type. In circuit design,
capacitors C1 and C2 that connect to the earth are added to the input and output terminals of the crystal
oscillator, respectively. The values of the two capacitors can be flexible, ranging from 6 pF to 22 pF. However,
the specific capacitive values of C1 and C2 depend on further tests and adjustments of the overall
performance of the whole circuit. Normally, the capacitive values ofC1 and C2 are within 10 pF when the
crystal oscillator frequency is 26 MHz, or 10 pF<C1 and C2<22 pF when the crystal oscillator frequency is 40
MHz.
The frequency of the RTC crystal oscillator is typically 32 kHz or 32.768 kHz. The accuracy can be out of the
range of ±20 PPM, when the internal calibration is applied to correct the frequency offset. When the chip