MEC1322 datasheet(313/456 Pages) MICROCHIP

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DS00001719D-page 313

MEC1322

DMA controller then reads the received byte from the GP-SPI’s SPI RX Data Register (SPIRD) and stores it in the DMA

receive buffer. With AUTO_READ set, this read clears both the RxBF and TxBE. Clearing TxBE causes (dummy) data

from the SPI TX Data Register (SPITD) to be transferred to the internal shift register, mimicking the effect of the afore-

mentioned write to the SPI TX Data Register (SPITD) by the driver. SPI clock is toggled again to shift in the second read

byte. This process continues until the end of the DMA buffer is reached - the DMA controller stops responding to an

active Tx Empty until the buffer’s address registers are reprogrammed.

27.10.3

TYPES OF SPI TRANSACTIONS

The GP-SPI controller can be configured to operate in three modes: Full Duplex, Half Duplex, and Dual Mode.

27.10.3.1

Full Duplex

In Full Duplex Mode, serial data is transmitted and received simultaneously by the SPI master over the SPDOUT and

SPDIN pins. To enable Full Duplex Mode clear SPDIN Select.

When a transaction is completed in the full-duplex mode, the RX_DATA shift register always contains received data

(valid or not) from the last transaction.

27.10.3.2

Half Duplex

In Half Duplex Mode, serial data is transmitted and received sequentially over a single data line (referred to as the SPD-

OUT pin). To enable Half Duplex Mode set SPDIN Select to 01b. The direction of the SPDOUT signal is determined by

the BIOEN bit.

• To transmit data in half duplex mode set the BIOEN bit before writing the TX_DATA register.

• To receive data in half duplex mode clear the BIOEN bit before writing the TX_DATA register with a dummy byte.

27.10.3.3

Dual Mode of Operation

In Dual Mode, serial data is transmitted sequentially from the SPDOUT pin and received in by the SPI master from the

SPDOUT and SPDIN pins. This essentially doubles the received data rate and is often available in SPI Flash devices.

To enable Dual Mode of operation the SPI core must be configured to receive data in path on the SPDIN1 and SPDIN2

inputs via SPDIN Select. The BIOEN bit determines if the SPI core is transmitting or receiving. The setting of this bit

determines the direction of the SPDOUT signal. The SPDIN Select bits are configuration bits that remain static for the

duration of a dual read command. The BIOEN bit must be toggled to indicate when the SPI core is transmitting and

receiving.

• To transmit data in dual mode set the BIOEN bit before writing the TX_DATA register.

• To receive data in dual mode clear the BIOEN bit before writing the TX_DATA register with a dummy byte. The

even bits (0,2,4,and 6) are received on the SPDOUT pin and the odd bits (1,3,5,and 7) are received on the SPDIN

pin. The hardware assembles these received bits into a single byte and loads them into the RX_DATA register

accordingly.

The following diagram illustrates a Dual Fast Read Command that is supported by some SPI Flash devices.

Note:

The Software driver must properly drive the BIOEN bit and store received data depending on the transac-

tion format of the specific slave device.

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