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Field
Name
R/W
Description
4
DC
R/W
Deferral Check
The deferral check function enables MAC. When the delay of the
transmitting state machine exceeds the mode of 24288 bits multiplied by
10 or 100 Mbps, the MAC will identify the frame aborted state, and set
the excessive delay error in the transmitted frame state.
When the bit is reset, the bit will disable the deferral check function until
the CRS signal becomes an invalid signal, and the MAC will be delayed.
This bit is applicable only in half-duplex mode.
6:5
BL
R/W
Back off Limit
This bit determines the random integer (r) of the time delay (4096-bit
time for 1000Mbps and 512-bit time for 10/100Mbps) that the MAC waits
before retransmission attempt when retrying after collision. This bit is
applicable only in half-duplex mode.
00
:
k=min(n
,
10)
01
:
k=min(n
,
8)
10
:
k=min(n
,
4)
11
:
k= min(n
,
1)
Wherein, n=the number of retransmission attempts. The value range of
random integer r is 0≤r
<
2k
7
ACS
R/W
Automatic Pad or CRC Stripping
Only when the bit length of MAC is less than 1536 bytes, will Pad or
FCS be removed when the frame comes in. All received frames with bit
length greater than or equal to 1536 bytes are passed to the application
program without removing Pad or FCS. When this bit is reset, the MAC
will transmit all incoming frames to the host without modification.
8
Reserved
9
DISR
R/W
Disable Retry
MAC will try to transmit once only. When a collision occurs to the MII
interface, the MAC will ignore transmission of the current frame and
report the abortion of a frame with a large collision error in the
transmitted frame state. When this bit is reset, retry the MAC according
to the setting of BL bit. This bit is applicable only in half-duplex mode.
10
IPC
R/W
IPv4 Checksum Offload
The MAC calculates all 16-bit 1 complement sum of all received
Ethernet frame payloads. It also checks whether the IPv4 header
checksum of the received Ethernet frame is correct, and gives the state
in the receiving state word. This function is disabled when this bit is
reset.
11
DM
R/W
Duplex Mode
MAC works in full-duplex mode and can transmit and receive at the
same time.
12
LBM
R/W
Loopback Mode
When this bit is set, the MAC will run in loopback mode on the MII. The
MII receive clock input (RX_CLK) needs to work in loopback mode
normally, because there is no loopback in the transmit clock.