CD2401 Intel, CD2401 Datasheet - Page 49

• Manufacturer Part Number: CD2401
• Description: Multi-protocol Communications Controller
• Manufacturer: Intel

5.4.6
Datasheet
Figure 7. Transmitter A and B Buffers
NOTE: The number of bits in each register is shown in parentheses (). Buffer A and buffer B do not
Synchronous Transmitter Examples
In
A/BTBADR, TCBADR, A/BTBCNT, and A/BTBSTS) is inside the CD2401.
Example 1
Transmit a frame out of channel 1 — no chaining.
1. The host checks the Ntbuf bit (DMABSTS[3]) for channel 1 to determine which buffer is next.
2. The host sets up the buffer data, the starting address — ATBADR, and the buffer byte count —
3. The host sets up the ATBSTS register. The EOF bit is set to indicate that there is no chaining.
4. The CD2401 starts frame transmission out of channel 1. When transmission is started, the
5. The CD2401 completes frame transmission by adding any necessary CRCs and trailing-frame
6. When the CD2401 completes the transmission, it clears the Tbusy bit. Then it sets the EOB bit
Figure
need to be the same length.
In this example, Ntbuf is set to ‘0’ indicating that buffer A is used next.
ATBCNT.
The 2401own bit is set to give ownership to the CD2401. By setting 2401own, the host
commands the CD2401 to start transmission. Thus, everything must be ready (starting address,
buffer data, byte count) prior to setting 2401own.
CD2401 sets Tbusy bit (DMABSTS[2]). As transmission progresses, the current buffer pointer
(TCBADR) is updated by the CD2401. Also, at the start of transmission the Ntbuf bit is set to
‘1’ to notify the host that buffer B is next.
delimiters.
and clears the 2401own bit (ATBSTS[0]). This notifies the host that the transmission is
complete, and the CD2401 returns ownership of the buffer back to the host.
7, buffers A and B are contained in RAM external to the CD2401. All else (DMABSTS,
CD2401 TRANSMIT
DMA REGISTERS
(Currently using Buffer A)
ATBADR (32)
TABADR (32)
BTBADR (32)
ATBCNT (16)
BTBCNT (16)
ATBSTS (8)
BTBSTS (8)
(Status Register)
(Status Register)
Starting Address
Starting Address
Buffer Byte Count
Current Count
Buffer Byte Count
Multi-Protocol Communications Controller — CD2401
PHYSICAL
MEMORY
Transmit
Transmit
Buffer
Buffer
A
B
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