I could not understand your first query... wot exactly are do you want to know about those movx commands? Basically they are used to address external memory... but if you want some more information about them, check out the tutorial on this site.

However, as for the serial communication, the 8051 provides only a single byte buffer. As soon as you write to this buffer, (mov sbuf, some_data) it starts transmitting. You have to poll a certain bit (TI) in the SCON SFR to check if the byte has finished transmitting. Once TI is set, you can continue writing the next byte.

If you want a buffer of 5 bytes, you will have to implement it yourself. You should make the operation is interrupt-based, and you would need to use indirect addressing.

Check the tutorials on this site, they are very easy to understand.

kundi