Rabbit Rabbit 4000, User Manual

Page: 167 / 358

Chapter 17 Serial Ports E – F 157
Serial Port x Status Register (SESR) (Address = 0x00CB)
(HDLC Mode Only) (SFSR) (Address = 0x00DB)
Bit(s) Value Description
7 0 The receive data register is empty
1
There is a byte in the receive buffer. The serial port will request an interrupt
while this bit is set. The interrupt is cleared when the receive buffer is empty.
6,4 00 The byte in the receive buffer is data.
01 The byte in the receive buffer was followed by an abort.
10 The byte in the receive buffer is the last in the frame, with valid CRC.
11 The byte in the receive buffer is the last in the frame, with a CRC error.
5 0 The receive buffer was not overrun.
1 The receive buffer was overrun. This bit is cleared by reading the receive buffer.
3 0 The transmit buffer is empty.
1
The transmit buffer is not empty. The serial port will request an interrupt when
the transmitter takes a byte from the transmit buffer, unless the byte is marked as
the last in the frame. Transmit interrupts are cleared when the transmit buffer is
written, or when any value (which will be ignored) is written to this register.
2:1 00 Transmit interrupt due to buffer empty condition.
01
Transmitter finished sending CRC. An interrupt is generated at the end of the
CRC transmission. Data written in response to this interrupt will cause only one
flag to be transmitted between frames, and no interrupt will be generated by this
flag.
10
Transmitter finished sending an abort. An interrupt is generated at the end of an
abort transmission.
11
The transmitter finished sending a closing flag. Data written in response to this
interrupt will cause at least two flags to be transmitted between frames.
0 0 The byte in the receiver buffer is 8 bits.
1 The byte in the receiver buffer is less than 8 bits.