How do you send write requests to peripherals in code?
Assuming that you are writing code for a GAP Central and GATT Client device, use the API CyBle_GattcWriteCharacteristicValue() to send a write request to peripheral with whom you are connected.
Refer the project at following location to implement such an application:
Another question: how can this be used to write to multiple peripherals simultaneously?
To write to multiple peripherals simultaneously, you need to maintain multiple connections simultaneously with these peripherals. Multiple connections is not supported by the device.
Rather, you can use a star network to connect -> send data -> disconnect with one device and then continue it to others. Refer the time multiplexed Central project at following location: