MK50H25PLCC datasheet(37/64 Pages) STMICROELECTRONICS

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4.3.1.4 Receive Message Descriptor 3 (RMD3)

BIT

NAME

DESCRIPTION

15:00

MCNT

Message Byte Count is the length, in bytes, of the received frame

MCNT is valid only when ELF is set to a one. MCNT is written by

MK50H25 and read by the Host. If ELF is set to a zero the entire

buffer has been

utilized and

the message byte count is given in

BCNT above. The value of this field is expressed in two’s comple-

ment. MCNT also reflects additional FCS bytes if FCSEN = 1.

4.3.2 Transmit Message Descriptor Entry

4.3.2.1 Transmit Message Descriptor 0 (TMD0)

BIT

NAME

DESCRIPTION

OWNA

When this bit is a zero either the HOST or an I /O Acceleration Processor

owns this descriptor.

When this bit is a one the MK50H25 owns this

descriptor. The host sets the OWNA bit after filling the buffer pointed

to by the descriptor entry. The MK50H25 releases the descriptor after

transmitting the buffer and receiving

the proper acknowledgement

from the receiver. After the MK50H25, Host, or I/O Acceleration Proc-

essor has relinquished ownership of a buffer, it may not change any

field in the four words that comprise the descriptor entry.

OWNB

This bit determines whether the HOST or an I /O Acceleration Processor

owns the buffer when OWNA is a zero. The MK50H25 never uses this

bit. This bit is provided to facilitate use of I/O Acceleration processors.

SLF

Start of Long Frame indicates that this is the first buffer used by the

MK50H25 for this frame. It is used for data chaining buffers. SLF is set

by the Host. When not chaining, SLF should be set to a one.

NOTE: A ”Long Frame” is any frame which needs data chaining.

ELF

End of Long Frame indicates that this is the last buffer used by the

MK50H25 for this frame. It is used for data chaining buffers. If both

SLF and ELF were set the frame would fit into one buffer and no

data chaining would be required. ELF is set by the Host. When not

chaining, ELF should be set to a one.

MCNT<15:00>

TBADR<23:16>

MK50H25

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