Rabbit Rabbit 4000, User Manual

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210 Rabbit 4000 Microprocessor User’s Manual
The receive data input for the network port uses two pins, with the exact definition of the
two pins under program control (via NAPCR) according to the table below.
20.5 Register Descriptions
NAPCR[7:5] RXD+ RXD- Comment
000 RXD+ RXD- Normal differential input
010 RXD+ RXVAL True input with valid-data qualifier
100 RXD+ unused Single-ended true input data
110 RXD- unused Single-ended negative input data
xx1 RXD+ RXVAL
True input with valid-data qualifier;
RXD+ is XORd with NAPCR[7] and
RXD- is XORd with NAPCR[6] to provide
level inversion
Network Port A Data Register (NADR) (Address = 0x0200)
Bit(s) Value Description
7:0 Read
Returns the contents of the receive buffer. This register is not normally accessed
by the processor, but is accessed by the DMA channels.
Write Loads the transmit buffer with a data byte for transmission.
Network Port A Last Data Register (NALDR) (Address = 0x0201)
Bit(s) Value Description
7:0 Read
Returns the contents of the receive buffer. This register is not normally accessed
by the processor, but is accessed by the DMA.
Write
Loads the transmit buffer with the last data byte of a frame to enable the
subsequent transmission of the CRC. The DMA automatically writes the last
byte of the frame to this address.