CD2231 Intel Corporation, CD2231 Datasheet - Page 48

• Manufacturer Part Number: CD2231
• Description: CD2231 Intelligent Two-channel Lan And Wan Communications Controller
• Manufacturer: Intel Corporation

CD2231 — Intelligent Two-Channel LAN and WAN Communications Controller
48
Example 2
Transmit out of channel 0 and chain three buffers into one frame. The frame is 240 bytes long, and
the maximum buffer size is 100.
10. The CD2231 continues transmission of the current frame, but now transmission is from Buffer
11. After the CD2231 has completed transmission of the second link out of Buffer A, it sets the
5. The CD2231 completes frame transmission by adding any necessary CRCs and trailing frame
6. When the CD2231 completes the transmission, it clears the Tbusy bit. Then, it sets the EOB
7. The CD2231 optionally interrupts the host, with EOF and EOB in the TISR both set to indicate
1. The host checks the Ntbuf bit in the DMABSTS register for channel 0 to determine which
2. The host sets up the buffer data, the starting address (BTBADR), and the buffer byte count
3. The host sets up the BTBSTS (‘B’ Buffer Status) register. The EOF bit is cleared to indicate
4. At this point, the host has enough time to transmit 100 bytes to set up the next buffer link. If
5. The CD2231 starts transmitting Buffer B from channel 0. When this is started, the Ntbuf bit is
6. At the end of transmission of this buffer, the CD2231 does not add any CRCs nor end of frame
7. After the CD2231 has completed transmission of the first link out of Buffer B, the CD2231
8. The CD2231 optionally interrupts the host with EOF clear and EOB set in the TISR to indicate
9. The ATBSTS register indicates that the CD2231 has ownership of Buffer A for transmission of
delimiters.
bit and clears the 2231own bit in the ATBSTS. This notifies the host that the transmission is
complete, and returns ownership of the buffer back to the host.
that the transmission is complete and there was no chaining.
buffer is next. In this example, Ntbuf is set to ‘1’ indicating that Buffer B is used next.
(BTBCNT) for the first ‘link’ of the chain to be transmitted. For this example, BTBCNT is set
to ‘100’.
that this buffer is the first link in a chain. The 2231own bit is set to give ownership to the
CD2231. By setting 2231own, the host commands the CD2231 to start transmission. Thus,
everything must be ready (starting address, buffer, and data count) prior to setting 2231own.
the host fails to do this in time, there is a transmitter underrun, and the frame is aborted in
HDLC.
cleared to ‘0’ to indicate that Buffer A is next. This helps the host keep track of which buffer is
next. As transmission progresses, the current buffer pointer, TCBADR, is updated by the
CD2231. During or prior to this update, the host has readied Buffer A. For Buffer A, the EOF
bit in the ATBSTS register is cleared by the host, indicating that the buffer is not at the end of
the chain.
delimiters because there is more data for the current frame.
sets the EOB bit and clears the 2231own bit in the BTBSTS. This notifies the host that the
transmission is complete, and returns ownership of the buffer back to the host.
that the transmission is completed, and that there was chaining.
the next ‘link’. The EOF is cleared so that this link is not the last link in the transmitted chain.
A. This is the second link, which is 100 bytes long. During this time, the host must set up a
new Buffer B for the third and final link. The BTBCNT for the last link is set to 40 bytes.
EOB bit and clears the 2231own bit in the ATBSTS. This notifies the host that the
transmission has complete, and returns ownership of the buffer back to the host. As with the
first link, the CD2231 does not add CRCs or ending frame delimiters to this link.
Datasheet