668-0003-C Rabbit Semiconductor, 668-0003-C Datasheet - Page 133

• 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

made to the shift register, a new byte can be loaded into the transmit register and a new
send code can be stored.
To receive a byte in external clock mode, the user must set the receive code for the first
byte and then store the receive code for the next byte after each byte is removed from the
data register. Since the receive code must be stored before the transmitter sends the next
byte, the receiver must service the interrupt within 1/2 baud clock to maintain full-speed
transmission. This is usually not practical unless a flow control arrangement is made or the
transmitter inserts gaps between the clock bursts.
In order to carry on high-speed communication, the best arrangement will usually be for
the receiver to provide the clock. When the receiver provides the clock, the transmitter
should always be able to keep up because it is double-buffered and has a full character
time to answer the transmitter data register empty interrupt. The receiver will answer
interrupts that are generated on the last clock rising edge. If the interrupt can be serviced
within 1/2 clock, there will be no pause in the data rate. If it takes the receiver longer to
answer, then there will be a gap between bytes, the length of which depends on the inter-
rupt latency. For example, if the baud rate is 400,000 bps, then up to 50,000 bytes per sec-
ond could be transmitted, or a byte every 20 µs. No data will be lost if the transmitter can
answer its interrupts within 20 µs. There will be no slow down if the receiver can answer
its interrupt within 1/2 clock or 1.25 µs. If it can answer within 1.5 clocks, or 2.75 µs, the
data rate will slow to 44,444 bytes per second. If it can answer in 2.5 clocks or 6.25 µs, the
data rate slows to 40,000 bytes per second. If it can answer in 3.5 clocks or 8.75 µs, the
data rate will slow to 36,363 bytes per second, and so forth.
If two-way half-duplex communication is desired, the clock can be turned around so that
the receiver always provides the clock. This is slightly more complicated since the
receiver cannot initiate a message. If the receiver attempts to receive a character and the
transmitter is not transmitting, the last bit sent will be received for all eight bits.
Chapter 12 Rabbit Serial Ports
127