Data Sheet

!
!
Espressif Systems
ESP8266 Datasheet
2.5. MCU
ESP8266EX is embedded with Tensilica L106 32-bit micro controller (MCU), which features extra low
power consumption and 16-bit RSIC. The CPU clock speed is 80MHz. It can also reach a maximum
value of 160MHz. Real Time Operation System (RTOS) is enabled. Currently, only 20% of MIPS has
been occupied by the WiFi stack, the rest can all be used for user application programming and
development. The following interfaces can be used to connect to the MCU embedded in
ESP8266EX:
Programmable RAM/ROM interfaces (iBus), which can be connected with memory controller,
and can also be used to visit external flash;
Data RAM interface (dBus), which can connected with memory controller;
AHB interface, can be used to visit the register.
2.6. Memory Organization
2.6.1. Internal SRAM and ROM
ESP8266EX WiFi SoC is embedded with memory controller, including SRAM and ROM. MCU can visit
the memory units through iBus, dBus, and AHB interfaces. All memory units can be visited upon
request, while a memory arbiter will decide the running sequence according to the time when these
requests are received by the processor.
According to our current version of SDK provided, SRAM space that is available to users is assigned
as below:
RAM size is around 50 KB, that is to say, when ESP8266EX is working under the station mode
and is connected to the router, programmable space accessible to user in heap and data section
is around 50 KB.)
There is no programmable ROM in the SoC, therefore, user program must be stored in an
external SPI flash.
2.6.2. External SPI Flash
An external SPI flash is used together with ESP8266EX to store user programs. Theoretically
speaking, up to 16 Mbyte memory capacity can be supported.
Suggested SPI Flash memory capacity:
OTA is disabled: the minimum flash memory that can be supported is 512 KB;
OTA is enabled: the minimum flash memory that can be supported is 1 MB.
Several SPI modes can be supported, including Standard SPI, Dual SPI, DIO SPI, QIO SPI, and Quad
SPI.
Espressif Systems / August 1, 2015
15 31