208 Rabbit 2000 Microprocessor
Synchronous Serial Port
To initiate basic sending or receiving in the clocked serial mode, a command must be
issued by writing to bits (7,6) of the control register for each byte sent or received. There
is one command is to send a byte, and a different command to receive a byte. For full-
duplex communication, it is necessary that a Tx command be issued first, followed within
one-half bit time by the Rx command. The new feature added to revisions A–C contains a
command that initiates a transmit and receive at the same time for better support of full-
duplex communication.
Table B-8. Serial Port Control Register Ports A and B
Serial Port x Control Register (SACR) (Address = 0xC4)
(SBCR) (Address = 0xD4)
Bit(s) Value Description
7:6 00 No operation. These bits are ignored in the asynch mode.
01 In clocked serial mode, start a byte receive operation.
10 In clocked serial mode, start a byte transmit operation.
11
In clocked serial mode, start a byte transmit operation and a byte receive
operation simultaneously.
Only available in revisions A–C
5:4 00 Parallel Port C is used for input.
01 Parallel Port D is used for input.
1x Disable the receiver input.
3:2 00 Asynch mode with 8 bits per character.
01
Asynch mode with 7 bits per character. In this mode the most significant bit of a
byte is ignored for transmit, and is always zero in receive data.
10
Clocked serial mode with external clock.
Serial Port A clock is on Parallel Port PB1
Serial Port B clock is on Parallel Port PB0
11
Clocked serial mode with internal clock.
Serial Port A clock is on Parallel Port PB1
Serial Port B clock is on Parallel Port PB0
1:0 00 The Serial Port interrupt is disabled.
01 The Serial Port uses Interrupt Priority 1.
10 The Serial Port uses Interrupt Priority 2.
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