请问CC2540和CC2640有什么不同

你好，

回答你的问题

1.作为Master的时候，最大的连接个数有没有不同？

 CC2540最大3个 CC2640最大8个

2.连接上多个之后是同时进行数据交换还是轮流进行？这两种芯片在这个地方有什么不一样吗？

轮流进行，这个和蓝牙相关，和芯片无关。

3.CC2540有Dongle的例程，CC2640有吗？

CC2540作为dongle主要是CC2540带USB接口，如果你要做CC6240的dongle，可以加一个USB转串口芯片+CC2640.CC2640烧录hosttest的程序，可能需要你做少许修改。

4.其他比较重要的不同？

CC254x只支持BT4.1的协议栈，CC2640现在支持BT4.2协议栈。

蓝牙4.2的三大特性：

LE Secure Connections
Based on Diffie-Hellman Key Exchange, similar to the Secure Simple Pairing feature in classic Bluetooth
Closes the well-known security holes in BLE that exist in the BT 4.0/4.1 specs
LE Privacy 1.2

Keeps BLE devices from being tracked
Significant improvement over the confusing and little-used privacy features in BT 4.0/4.1 (which are being deprecated)

LE Data Length Extension
Increases data throughput by up to 2.5x by increasing the packet capacity by 10x