CD2231 Intel Corporation, CD2231 Datasheet - Page 51

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CD2231

Manufacturer Part Number
CD2231
Description
CD2231 Intelligent Two-channel Lan And Wan Communications Controller
Manufacturer
Intel Corporation
Datasheet
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Datasheet
Example 2
Receive a frame on channel 0, which consists of three buffers chained together. The frame is 240
bytes long, and the maximum buffer size is 100.
10. After the CD2231 has received the second link into Buffer A, the CD2231 sets the EOB bit
12. By this time the host has set up a new buffer for Buffer B.
13. The CD2231 receives data into Buffer B in the same manner, as previously explained.
11. The CD2231 optionally interrupts the host with bit EOF clear and bit EOB set in the RISR to
6. The CD2231 sets the EOB and EOF bits. This notifies the host that the end of the buffer and
1. The host checks the Nrbuf bit (DMABSTS[1]) register for channel 0 to determine which
2. The host sets up the starting address — BRBADR. Buffer size is set to ‘100’ in this example.
3. The host then sets the 2231own bit to relinquish ownership to the CD2231.
4. The host should know the amount of time it takes to receive 100 bytes, because this is the
5. Suppose that the CD2231 starts receiving data into Buffer B of channel 0. When this is started,
6. After the CD2231 has received the first link of the frame into Buffer B, it sets the EOB bit and
7. The CD2231 optionally interrupts the host with bit EOF clear and bit EOB set in the RISR to
8. The ARBSTS register indicates that the CD2231 has ownership of Buffer A for transmission
9. As the frame continues to be received, the data goes into Buffer A. This is the second link,
size count — ARBCNT. The CD2231 writes the value of the actual received byte count into
the same register — ARBCNT. (Note that the host has written the maximum buffer size in
ARBCNT when the buffer is given to the CD2231. But when the buffer is returned back to the
host, the CD2231 has written the actual byte count of the received buffer into ARBCNT.)
frame have been reached. The CD2231 also clears the 2231own bit to return the buffer to the
host.
buffer is next. In this example, Nrbuf is set to ‘1’ indicating that Buffer B is used next.
Thus, the host sets BRBCNT to ‘100’.
minimum time the host has to set up the next buffer link. If the host fails to do this in time,
there is a receiver overrun, and the received frame is lost.
the Nrbuf bit is cleared to ‘0’ by the CD2231 to help the host keep track of which buffer is
next. (During or prior to this, the host has made Buffer A ready.)
clears the EOF bit. This indicates that the first link in a chain has been received. Also, the
CD2231 clears the 2231own bit, and returns ownership of the buffer to the host.
For the first received link, the received byte count (BRBCNT) remains unchanged at 100,
since the received data filled the buffer.
indicate that the received buffer is complete, and that there was chaining.
of the next link.
which is 100 bytes long. During this time, the host must set up a new Buffer B for the third and
final link.
and clears the 2231own bit in the ARBSTS. This returns ownership of the buffer to the host.
As with the first link, the received byte count — ARBCNT, remains unchanged at 100 since
the received data filled the buffer.
indicate that the received buffer is complete and that there was chaining.
Intelligent Two-Channel LAN and WAN Communications Controller — CD2231
51

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