MK5027DIP datasheet(7/19 Pages) STMICROELECTRONICS

7 / 19 page

All signal pins on the MK5027 are TTL compat-

ible. This has the advantage of making the

MK5027 in- dependent of the physical interface.

As shown in Figure 2. Iine drivers and receivers

are used for electrical- connection to the physical

layer.

SERIAL INTERFACE

The MK5027 provides two separate serial chan-

nels: one for received data and one for transmit-

ted data. These serial channels are completely

separate and may be run at different clock fre-

quencies The receiver is responsible for recogniz-

ing frame boundries. removal of inserted zeroes

(for transparency) and checking the incoming

FCS. Signal units with in correct FCS values are

discarded. The receiver also parallelizes the in-

coming data which is placed into the receive data

buffers within the receive descriptor ring The

transmitter is responsible for framing and serializ-

ing the data frames placed in the transmit de-

scriptor ring. The transmitter calculates the FCS

of the outgoing data and appends it to the data

The transmitter generates flag sequences for in-

ter-signal unit fill, at least two flags are transmit-

ted between adjacent signal units. The FCS cal-

culations for both directions of serial data

optionally follow either the 16 bit CRC CCITT or

the 32-bit CRC 32 algorithms FCS generation and

checking can also be optionally disabled if neces-

sary.

MICROPROCESSOR INTERFACE

The MK5027 contains a dual channel DMA on

chip to handle data transfers to and from the host

mem- ory. All access to the initialization block and

descriptor rings is handled in this way The ad-

dress bus is 24 bits wide and does not use any

segmentation or paging methods. Data transfers

can optionally be 8 and 16 bit operations. this al-

lows easy interfacing with both 8 and 16 bit proc-

essors DMA transfers can be up to 1. 8 or an un-

limited number of words per transfer under

program control During bus slave operation the

MK5027 allows access to its 6 control/status reg-

isters which are used to monitor and control the

chip. These registers are used to control link pro-

cedures, configure interface options, control and

monitor interrupt status. and more. Bus slave

mode also allows both 8 and 16 bit accesses.

BUFFER MANAGEMENT

The basic organization of the buffer management

is a circular queue of tasks in memory called de-

scriptor rings. There are separate rings to de-

scribe the transmit and receive operations. Up to

128 buffers may be queued-up on a descriptor

ring awaiting execution by the MK5027 The de-

scriptor ring has a segment assigned to each

buffer. Each segment holds a pointer for the start-

ing address of the buffer. and holds a value for

the length of the buffer in bytes.

Each segment also contains two control bits

called OWNA and OWNB, which denote whether

the MK5027. the HOST. or the l/O ACCELERA-

TION PROCESSOR (if present) ”owns” the buff-

er. For transmit. when the MK5027 owns the buff-

er. the MK5027 is allowed and commanded to

transmit the buffer When the MK5027 does not

own the buffer, it will not transmit that buffer. For

receive. when the MK5027 owns a buffer. it may

place received data into that buffer. Conversely.

when the MK5027 does

not own a receive buff-

er, it will not place received data in that buffer.

The MK5027 buffer management mechanism will

handly signal units which are longer than the

length of an individual buffer. This is done by a

chaining method which utilizes multiple buffers.

The MK5027 tests the next segment in the de-

scriptor ring in a ”look ahead” manner. If the

packet is too long for one buffer, the next buffer-

will be used after filling the first buffer: that is,

”chained”. The MK5027 will then ”look ahead” to

the next buffer, and chain that buffer if necessary,

and so on The operational parameters for the

buffer management are defined by the user

in the initialization block The parameters defined

include the basic mode of operation. the number

of entries for the transmitter and receiver descrip-

tor rings. etc.

MK5027

7/19

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