668-0003-C Rabbit Semiconductor, 668-0003-C Datasheet - Page 126

• Manufacturer Part Number: 668-0003-C
• Description: IC CPU RABBIT2000 30MHZ 100PQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 668-0003-C

• Rohs Status: RoHS non-compliant
• Processor Type: Rabbit 2000 8-Bit
• Speed: 30MHz
• Voltage: 2.7V, 3V, 3.3V, 5V
• Mounting Type: Surface Mount
• Package / Case: 100-MQFP, 100-PQFP
• Features: -
• Other names: 316-1004; 668-0003

12.1 Serial Port Register Layout
Figure 12-2 shows a functional block diagram of a serial port. Each serial port has a data
register, a control register and a status register. Writing to the data register starts transmis-
sion. If the write is performed to an alternate data register address, the extra address bit or
9th bit is sent. When data bits have been received, they are read from the data register. The
control register is used to set the transmit and receive parameters. The status register may
be tested to check on the operation of the serial port.
The clock input to the serial port unit must be 16 times the baud rate in the asynchronous
mode and 2 times the baud rate for the clocked serial mode when the internal clock is
used. Timers A4–A7 supply the input clock for Serial Ports A–D. These timers can divide
the frequency by any number from 1 to 256 (see Chapter 11). The input frequency to the
timers can be selected in different ways described in the documentation for the timers.
One choice is the peripheral clock divided by 2—with that choice and a well-chosen crys-
tal frequency for the main oscillator, the most commonly used baud rates can be obtained
down to approximately 2400 bps at the highest Rabbit clock frequencies (see Section A.4
in Appendix A).
120
Signals shown at microprocessor Tx pin
Rx serial data in
Start Bit
Start Bit
Tx
Tx
Bit
Bit
Input Shift Reg
Figure 12-2. Functional Block Diagram of a Serial Port
Data In Reg
0
0
0
0
1
1
1 1
1
Read Data
2
2
1
0
3
3
0
4
4
1
1
5
0
5
0
Output Shift Reg
9th bit
6
6
1
1
Data Out Reg
7
7
1
1
A
Rabbit 2000 Microprocessor User’s Manual
stop
Write Data
Stop Bit
stop
Transmitting 0x0D6
Stop Bit
Transmitting 0x0D6
with 9th address bit
Tx serial data out
Alt Data Out
(for 9th bit)