The number of full duplex UARTs that can be integrated in a PSoC1 device depends on the number of digital blocks available in the device. To implement a full duplex UART, 2 digital communication blocks are required. In the PSoC, half of the digital blocks are communication blocks. So, in a device with 4 digital blocks, 2 communication blocks are available and hence one UART may be implemented. In a device with 8 digital blocks, 2 UARTS may be implemented and in a device with 16 digital blocks 4 UARTs may be implemented.