Spi Overlap & Display Application Guide; Functional Overview - Espressif ESP8266 Technical Reference

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5.

5.1. Functional Overview

The Overlap mode of ESP8266 Host SPI allows for two SPI modes (SPI and HSPI) to reuse
the same IO interface (such as SCLK, MOSI and MISO) for the operation of multiple slave
SPI devices. The hardware supports 3 line chip selection. If there are additional 3 slave
devices, GPIO can be adopted as CS signal for the communication of multiple slave device.
Generally speaking, in order to ensure that the CPU can be running at high efficiency, SPI
module is used to read the running program from external Flash to CPU CACHE, while
HSPI module is used to operate slave devices of other users. Under Overlap mode, the
hardware will automatically arbitrate the control of two SPI modules to the current pin signal
for time-sharing application. If the software starts HSPI communication, the arbitration
signal will delay the start of HSPI block communication via the working of SPI. The
arbitration signal is then allowed to start the communication of HSPI IO interface after SPI
finishes reading the program codes for communication. This is illustrated in Figure 1. For
user software, only a switch of the corresponding CS signal before the start of
communicator is needed. Other operations are of no difference to the use of single HSPI
communication.
Espressif
SPI Overlap & Display
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Figure 5-1. SPI Overlap Block Diagram
5. SPI Overlap & Display Application Guide
Application Guide
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