External Bus Request Arbitration (Brq) - Fujitsu FR Series Application Note

DIRECT MEMORY ACCESS

Chapter 2 Direct Memory Access

When a device is operating in external bus extended mode, an external bus request (BRQ)

function can be used. Using BRQ pin any external peripheral can request to use the external

bus for the configured chip select area.

While the BRQ is asserted by any external device and the access is granted. Then such

external device controls the external bus and performs the data transfer. During such

transfer, if DMAC requires to use the external bus for the transfer, the DMAC has to wait

until the BRQ is active. Once BRQ is released the DMAC can use external bus.

If the DMAC is already using the external bus and the BRQ is asserted DMAC transfer is

temporarily stopped. Once BRQ is released the DMAC can use external bus.

If the DMAC transfer through the external bus and BRQ is simultaneous then DMAC waits till

the external device finishes transfer and then DMAC takes over.

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