at75c220 ATMEL Corporation, at75c220 Datasheet - Page 40

• Manufacturer Part Number: at75c220
• Description: Smart Internet Appliance Processor Siap
• Manufacturer: ATMEL Corporation

MAC Transmit Address Register
Register Name: ETH_TAR
Access Type: Read/write
Reset Value: 0x0
•
MAC Transmit Control Register
Register Name: ETH_TCR
Access Type: Read/write
Reset Value: 0x0
•
•
40
ADDRESS
LEN
NCRC
Transmit address register. Written with the address of the frame to be transmitted, read as the base address of the
buffer being accessed by the transmit FIFO. Note if the two least significant bits are not zero, transmit will start at the
byte indicated.
Transmit frame length. This register is written to the number of bytes to be transmitted excluding the four CRC bytes
unless the no CRC bit is asserted. Writing these bits to any non-zero value will initiate transmit. If the value is greater
than 1514 (1518 if no CRC is being generated), an oversize frame will be transmitted. This field is buffered so that a
new frame can be queued while the previous frame is still being transmitted. Must always be written in address-then-
length order. Reads as the total number of bytes to be transmitted (i.e., this value does not change as the frame is
transmitted.) Frame transmission will not start until two 32-bit words have been loaded into the transmit FIFO. The
length must be great enough to ensure two words are loaded.
No CRC. If this bit is set, it is assumed that the CRC is included in the length being written in the low-order bits and the
MAC will not append CRC to the transmitted frame. If the buffer is not at least 64 bytes long, a short frame will be sent.
This field is buffered so that a new frame can be queued while the previous frame is still being transmitted. Reads as
the value of the frame currently being transmitted.
NCRC
31
23
15
31
23
15
7
–
–
7
30
22
14
30
22
14
6
–
–
–
6
AT75C220
29
21
13
29
21
13
5
–
–
–
5
28
20
12
28
20
12
4
–
–
–
4
ADDRESS
ADDRESS
ADDRESS
ADDRESS
LEN
27
19
11
27
19
11
3
–
–
–
3
26
18
10
26
18
10
2
–
–
2
LEN
25
17
25
17
9
1
–
–
9
1
24
16
24
16
8
0
–
–
8
0