Compute number of data bits, according to memory address $0293.
Input: –
Output: X = Number of data bits.
Used registers: A, X.

Define RS232 as default output.
Input: A = 2.
Output: –
Used registers: A.

Write byte, from RS232 output cache at memory address $009E, to RS232.
Input: –
Output: –
Used registers: A, Y.

Define RS232 as default input.
Input: A = 2.
Output: –
Used registers: A.

Read byte from RS232.
Input: –
Output: A = Byte read.
Used registers: –

Wait for the end of RS232 transfer and disable RS232 interrupts. (So that the common chip registers can be used by serial bus or datasette input/output.)
Input: –
Output: –
Used registers: –

Read byte from RS232.
Input: –
Output: A = Byte read.
Used registers: A.

Read byte from RS232; retry on $00 byte.
Input: –
Output: A = Byte read.
Used registers: A.

Write byte to RS232.
Input: Carry = 0; A = Byte to write.
Output: –
Used registers: –

Close file on RS232; free RS232 input and output buffers, if exist.
Input: –
Output: –
Used registers: A, X, Y.

Open file on RS232; allocate RS232 input and output buffers, if do not exist.
Input: –
Output: –
Used registers: A, X, Y.

Initialize CIA #2 for opening/closing RS232.
Input: –
Output: –
Used registers: A, Y.