AM79C978A AMD [Advanced Micro Devices], AM79C978A Datasheet - Page 66
![no-image](/images/no-image-200.jpg)
AM79C978A
Manufacturer Part Number
AM79C978A
Description
Single-Chip 1/10 Mbps PCI Home Networking Controller
Manufacturer
AMD [Advanced Micro Devices]
Datasheet
1.AM79C978A.pdf
(256 pages)
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Part Number:
AM79C978AKC/W
Manufacturer:
AMD
Quantity:
20 000
Company:
Part Number:
AM79C978AKCW
Manufacturer:
AMD
Quantity:
6 605
- Current page: 66 of 256
- Download datasheet (4Mb)
Disable retry on collision (DRTY) is controlled by
the DRTY bit of the Mode register (CSR15) in the
initialization block.
Automatic pad field insertion is controlled by the
APAD_XMT bit in CSR4.
The disable FCS generation/transmission feature can
be programmed as a static feature or dynamically on a
frame-by-frame basis.
Transmit FIFO Watermark (XMTFW) in CSR80 sets
the point at which the BMU requests more data from
the transmit buffers for the FIFO. A minimum of
XMTFW empty spaces must be available in the trans-
mit FIFO before the BMU will request the system bus in
order to transfer transmit frame data into the transmit
FIFO.
Transmit Start Point (XMTSP) in CSR80 sets the
point when the transmitter actually attempts to trans-
mit a frame onto the media. A minimum of XMTSP
bytes must be written to the transmit FIFO for the
current frame before transmission of the current
frame will begin. (When automatically padded pack-
ets are being sent, it is conceivable that the XMTSP
is not reached when all of the data has been trans-
ferred to the FIFO. In this case, the transmission will
begin when all of the frame data has been placed
into the transmit FIFO.) The default value of XMTSP
is 01b, meaning there has to be 64 bytes in the trans-
mit FIFO to start a transmission.
Automatic Pad Generation
Transmit frames can be automatically padded to ex-
tend them to 64 data bytes (excluding preamble). This
allows the minimum frame size of 64 bytes (512 bits)
for IEEE 802.3/Ethernet to be guaranteed with no soft-
ware intervention from the host/controlling process.
Setting the APAD_XMT bit in CSR4 enables the auto-
matic padding feature. The pad is placed between the
LLC data field and FCS field in the IEEE 802.3 frame.
FCS is always added if the frame is padded, regardless
of the state of DXMTFCS (CSR15, bit 3) or ADD_FCS
(TMD1, bit 29). The transmit frame will be padded by
.
66
1010....1010
Preamble
Bits
56
10101011
SFD
Bits
8
Figure 35. ISO 8802-3 (IEEE/ANSI 802.3) Data Frame
Destination
Address
Bytes
6
Am79C978A
Address
Source
Bytes
6
bytes with the value of 00h. The default value of
APAD_XMT is 0, which will disable automatic pad gen-
eration after H_RESET.
It is the responsibility of upper layer software to cor-
rectly define the actual length field contained in the
message to correspond to the total number of LLC data
bytes encapsulated in the frame (length field as defined
in the ISO 8802-3 (IEEE/ANSI 802.3) standard). The
length value contained in the message is not used by
the Am79C978A controller to compute the actual num-
ber of pad bytes to be inserted. The Am79C978A con-
troller will append pad bytes dependent on the actual
number of bits transmitted onto the network. Once the
last data byte of the frame has completed, prior to ap-
pending the FCS, the Am79C978A controller will check
to ensure that 544 bits have been transmitted. If not,
pad bytes are added to extend the frame size to this
value, and the FCS is then added. See Figure 35.
The 544 bit count is derived from the following:
The 544 bit count is derived from the following:
At the point that FCS is to be appended, the transmitted
frame should contain:
A m i n i m u m l e n g t h t r a n s m i t f r a m e f r o m
theAm79C978A controller, therefore, will be 576 bits
after the FCS is appended.
Length
Bytes
2
Preamble/SFD + (Min Frame Size - FCS)
64 + (512-32) = 544 bits
Minimum frame size (excluding preamble/SFD,
including FCS)
Preamble/SFD size 8 bytes
FCS size
Minimum frame size (excluding preamble/SFD,
including FCS)
Preamble/SFD size 8 bytes
FCS size
Data
LLC
46 – 1500
Bytes
Pad
64 bytes
4 bytes
64 bytes
4 bytes
512 bits
64 bits
32 bits
512 bits
64 bits
32 bits
FCS
Bytes
4
22399A-38
Related parts for AM79C978A
Image
Part Number
Description
Manufacturer
Datasheet
Request
R
![AMD-751AC](/images/manufacturer_photos/0/0/14/advanced_micro_devices_tmb.jpg)
Part Number:
Description:
AMD-751ACAMD-751-TM System Controller Revision Guide
Manufacturer:
Advanced Micro Devices
Datasheet:
![AMD-751](/images/manufacturer_photos/0/0/14/advanced_micro_devices_tmb.jpg)
Part Number:
Description:
AMD-751AMD-751-TM System Controller Revision Guide
Manufacturer:
Advanced Micro Devices
Datasheet:
![AMD-X5-133SFZ](/images/manufacturer_photos/0/0/14/advanced_micro_devices_tmb.jpg)
Part Number:
Description:
AMD-X5-133SFZAm5X86? Microprocessor Family
Manufacturer:
Advanced Micro Devices
Datasheet:
![AMD-8131BLC](/images/manufacturer_photos/0/0/14/advanced_micro_devices_tmb.jpg)
Part Number:
Description:
Hyper Transport PCI-X Tunnel
Manufacturer:
Advanced Micro Devices
Datasheet:
![AMD-8111AC](/images/manufacturer_photos/0/0/14/advanced_micro_devices_tmb.jpg)
Part Number:
Description:
HyperTransport I/O Hub
Manufacturer:
Advanced Micro Devices
Datasheet:
![AMD-640AC](/images/manufacturer_photos/0/0/14/advanced_micro_devices_tmb.jpg)
Part Number:
Description:
System Controller
Manufacturer:
Advanced Micro Devices
Datasheet:
![AMD-K6](/images/no-image3.png)
Part Number:
Description:
AMD-K6 Processor
Manufacturer:
AMD [Advanced Micro Devices]
Datasheet:
![AMD-K6-2E/400AFR](/images/no-image3.png)
Part Number:
Description:
AMD-K6™-2E Embedded Processor
Manufacturer:
AMD [Advanced Micro Devices]
Datasheet:
![AMD-8132BLCT](/images/manufacturer_photos/0/0/44/amd__advanced_micro_devices__tmb.jpg)
Part Number:
Description:
Manufacturer:
AMD (ADVANCED MICRO DEVICES)
Datasheet:
![AMD-K6-IIIE+550ACR](/images/manufacturer_photos/0/0/44/amd__advanced_micro_devices__tmb.jpg)
Part Number:
Description:
Manufacturer:
AMD (ADVANCED MICRO DEVICES)
Datasheet:
![AMD-766AC](/images/no-image3.png)
Part Number:
Description:
Peripheral Bus Controller
Manufacturer:
AMD [Advanced Micro Devices]
Datasheet: