ENC424J600-I/ML Microchip Technology, ENC424J600-I/ML Datasheet - Page 107

• Manufacturer Part Number: ENC424J600-I/ML
• Description: IC ETHERNET CTRLR W/SPI 44-QFN
• Manufacturer: Microchip Technology

Specifications of ENC424J600-I/ML

• Package / Case: 44-QFN
• Controller Type: Ethernet Controller
• Interface: SPI
• Voltage - Supply: 3 V ~ 3.6 V
• Current - Supply: 96mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Input Voltage Range (max): 5.5 V
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Operating Supply Voltage: 3 V to 3.6 V
• Supply Current (max): 117 mA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: AC164132 - BOARD DAUGHTER PICTAIL ETHERNET
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

11.0
Flow control provides a mechanism for network
stations to temporarily stop transmission of data to
themselves. This feature is commonly used to prevent
buffer overruns while receiving data.
ENC424J600/624J600 devices are capable of both
automatic and manual flow control. The hardware can
advertise when it is temporarily unable to receive data
and delay transmissions when a remote system does
the same. Flow control is supported for both full and
half-duplex links. It can either be initiated manually by
software, or configured to enable automatically when
insufficient space remains in the receive buffer
memory.
Flow control operation is configured by the FCOP<1:0>
bits (ECON1<7:6>), the AUTOFC bit (ECON2<7>), the
RXPAUS and PASSALL bits (MACON1<2:1>), and the
EPAUS and ERXWM registers in some modes.
11.1
Flow control operation differs between full and
half-duplex links. Both modes are supported, but it is
important to understand the difference before enabling
flow control in an application.
11.1.1
When the link is operating in Half-Duplex mode, flow
control operates by jamming the network. The node
wishing to inhibit transmissions to itself sends a
preamble pattern of alternating ones and zeros (55h)
on the medium; this is also known as asserting back
pressure on the link. Since the link is operating under
Half-Duplex mode, all connected nodes must wait
before transmitting. If a node does transmit, compliant
nodes will detect the collision and wait until the
jamming stops to retransmit. This effectively jams the
network until flow control is disabled.
If a frame is to be transmitted while flow control is
enabled, the ENCX24J600 will stop jamming, wait the
standard Inter-Packet Gap (IPG) delay, then attempt to
transmit. Because all traffic was previously jammed,
several nodes may begin transmitting and several
collisions may occur. The hardware will transmit and
resume jamming as soon as possible, but it is feasible
for other nodes to transmit packets before this
happens. This limitation of flow control in half-duplex
operation cannot be avoided.
 2010 Microchip Technology Inc.
Note:
FLOW CONTROL
Modes of Operation
Flow control is an optional portion of the
IEEE 802.3 specification and may not be
implemented on all remote devices.
HALF-DUPLEX MODE
ENC424J600/624J600
Given the detrimental effect that back pressure based
flow control inflicts on a network, along with the
possible lack of effectiveness, it is recommended that
flow control be avoided in Half-Duplex mode unless the
application is used in a closed network environment
with proper testing.
When
FCOP<1:0> to ‘ 00 ’ disables the flow control. Any other
combination enables flow control and causes the
device to jam the network.
11.1.2
Flow control for full-duplex links is much more robust.
Instead of jamming the network, a station can send a
pause control frame to the remote system. The pause
frame is directed to a special Multicast destination
address (01-08-C2-00-00-01) and indicates how long
the remote node should wait before transmitting again.
This time is expressed in units of pause quanta, where
one pause quanta is equal to 512 bit times.
While a station is silenced or paused, reception is still
enabled. If another pause control frame arrives, any
previous value is discarded and the timer restarts using
the new pause time value. If the received control frame
has a timer value of zero, the pause is terminated and
transmission resumes immediately.
When operating in Full-Duplex mode, each combina-
tion of FCOP<1:0> has a different effect on transmitting
control frames. These combinations are discussed in
Section 11.2.1 “Manual Flow Control” .
11.1.3
The ENCX24J600 automatically processes incoming
pause control frames without application intervention.
When a pause control frame is received, the MAC
internally sets the pause timer. Transmission is inhib-
ited while the timer is active. If an application attempts
to transmit a packet during this time, the transmission
logic will stall until the time expires (i.e., TXRTS will
stay set for longer than normal).
Pause control frames are normally filtered out by the
MAC and are not written to the receive buffer. Setting the
PASSALL bit (MACON1<1>) alters this behavior and
causes these frames to pass through the receive filters.
If the frame is accepted, it will be written to the receive
buffer. However, setting PASSALL will also cause the
MAC to not process the pause control frame. The trans-
mission logic will allow immediate transmission without
regard to the remote pause requests.
Before using either automatic or manual flow control,
set the pause time value with the EPAUS register. This
value controls the pause time value that is transmitted
with each pause control frame. Each unit of pause
quanta in this register is equal to 512 bit times.
operating
FULL-DUPLEX MODE
TRANSMITTING AND RECEIVING
PAUSE CONTROL FRAMES
in
Half-Duplex
DS39935C-page 105
mode,
setting