A very useful feature provided by the DS80C320 is the availability of a second serial port (UART). The second serial port functions almost identically to the original port with its own set of SFRs to control it. Both serial ports may be used simultaneously and may operate at different baud rates.
The original serial port is referred to as serial port 0 and the new secondary port is referred to as serial port 1. All SFRs that are related to serial communications are appended with a "0" in the case of serial port 0 and with a "1" in the case of serial port1. Thus, the 8052s SBUF SFR is now called SBUF0 and the DS80C320s new SFR to read and write from its secondary port is called SBUF1. At the hardware level, P1.2 (RXD1) is used for reception of data on serial port 1 and P1.3 (TXD1) is used for the transmission of data.
The control of the new serial port is identical to the original 8052 serial port, but you must use the SFRs that control the new port. They are:
| Original Serial Port SFR | Secondary Serial Port SFR | Secondary Serial Port SFR Address |
| SCON | SCON1 | C0h |
| SBUF | SBUF1 | C1h |
Note that while the 8052s standard serial port can use either Timer 1 or Timer 2 to generate baud rates, the secondary serial port on the DS80C320 may only use Timer 1. However, both serial ports may use timer 1 simultaneously if so desired.
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