AX88796BLI ASIX [ASIX Electronics Corporation], AX88796BLI Datasheet - Page 19

• Manufacturer Part Number: AX88796BLI
• Description: Low-pin-count Non-PCI 8/16-bit 10/100M Fast Ethernet Controller
• Manufacturer: ASIX [ASIX Electronics Corporation]

Transmit Packet Assembly
The AX88796B requires a contiguous assembled packet with the format shown below. The transmit byte count
includes the Destination Address, Source Address, Length Field and Data. It does not include preamble and CRC.
When transmitting data smaller than 64 bytes, AX88796B can auto padding to a minimum length of 64 bytes
Ethernet frame. The packets are placed in the buffer RAM by the system. System programs the AX88796B Core's
Remote DMA to move the data from the system buffer RAM to internal transmit buffer RAM.
The data transfer must be 16-bits (1 word) when in 16-bit mode, and 8-bits when the AX88796B Controller is set in
8-bit mode. The data width is selected by setting the WTS bit in the Data Configuration Register.
Transmission
Prior to transmission, the TPSR (Transmit Page Start Register) and TBCR0, TBCR1 (Transmit Byte Count
Registers) must be initialized. To initiate transmission of the packet the TXP bit in the Command Register is set. The
Transmit Status Register (TSR) is cleared and the AX88796B begins to pre-fetch transmit data from memory. If the
Inter-packet Gap (IPG) has timed out the AX88796B will begin transmission.
Conditions Required To Begin Transmission
In order to transmit a packet, the following three conditions must be met:
1. The Inter-packet Gap Timer has timed out
2. At least one byte has entered the FIFO.
3. If a collision had been detected then before transmission the packet back-off time must have timed out.
Collision Recovery
During transmission, the Buffer Management logic monitors the transmit circuitry to determine if a collision has
occurred. If a collision is detected, the Buffer Management logic will reset the FIFO and restore the Transmit DMA
pointers for retransmission of the packet. The COL bit will be set in the TSR and the NCR (Number of Collisions
Register) will be incremented. If 15 retransmissions each result in a collision the transmission will be aborted and
the ABT bit in the TSR will be set.
General Transmit Packet Format
Destination Address
Source Address
Length / Type
Data
(Pad if < 46 Bytes)
6 Bytes
6 Bytes
2 Bytes
46 Bytes
Min.
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AX88796BLF / AX88796BLI
ASIX ELECTRONICS CORPORATION