59628957701XA View Datasheet(PDF) - Aeroflex UTMC

Part Name

Description

Manufacturer

59628957701XA

BCRTM

Aeroflex UTMC 

A receive descriptor and a transmit descriptor are associated

with each subaddress. The descriptors reside in memory and

are listed sequentially by subaddress. By using the index

within the descriptor, the BCRTM can buffer incoming and

outgoing messages, which reduces host CPU overhead.

This message buffering also reduces the risk of incoming

messages being overwritten by subsequent incoming

messages.

Each descriptor contains a programmable interrupt structure

for subsystem notification of user-selected message

transfers and indicates when the message buffers are full.

Illegalizing subaddresses, in normal and broadcast modes,

is accomplished by using programmable bits within the

descriptor (see the RT Functional Operation section on

this page).

Message Status information -- including word count, an

internally generated time tag, and broadcast and message

validity information -- is provided for each message. The

Message Status Words are stored in a separate Message

Status Word list according to subaddress. The list’s starting

locations are programmable within the descriptor.

Message data, received or transmitted, is also stored in lists.

The message capacity of the lists and the lists’ locations are

user selectable within the descriptor.

6.1 RT Functional Operation

The RT off-loads the host computer of all routine data

transfers involved with message transfers over the 1553B

bus by providing a wide range of user-programmable

functions. These functions make the BCRTM’s operation

flexible for a variety of applications. The following

paragraphs give each function’s operational descriptions.

6.1.1 RT Subaddress Descriptor Definition

The host sets words within the descriptor (see figure 6). The

BCRTM then reads the descriptor words when servicing a

command corresponding to the specified descriptor. All bit-

selectable functions are active high and inhibited when low.

A. Control Word. The first word in the descriptor, the Control Word, selects or disables message transfers and selects an index.

Bit

Number

Description

BITs

15-11

Reserved.

BIT 10

Illegal Broadcast Subaddress. Indicates to the BCRTM not to access this subaddress using broadcast

commands. The Message Error bit in the status word is set if the illegal broadcast subaddress is addressed.

Since transmit commands do not apply to broadcast, this bit applies only to receive commands.

BIT 9

Illegal Subaddress. Set by the host CPU, it indicates to the BCRTM that a command with this subaddress is

illegal. If a command uses an illegal subaddress the Message Error bit in the 1553 status word is set. The Illegal

Command Interrupt is also asserted if enabled.

BIT 8

Interrupt Upon Valid Command Received. Indicates that the BCRTM is to assert an interrupt every time a

command addresses this descriptor. The interrupt occurs just prior to post-command descriptor updating.

BIT 7

Interrupt When Index = 0. Indicates that the BCRTM initiates an interrupt when the index is decremented

to zero.

BITs 6-0

Index. These bits are for indexed message buffering. Indexing means transacting a pre-specified number of

messages before notifying the host CPU. After each message transaction, the BCRTM decrements the index by

one until index = 0. Note that the index is decremented for messages that contain message errors.

B. Message Status List Pointer. The host sets the Message Status List Pointer, the second word within the descriptor, and the

BCRTM uses it as a starting address for the Message Status List. It is incremented by one with each Message Status Word

write. If the Control Word Index is already equal to zero, the Message Status List Pointer is not incremented and the previous

Message Status Word is overwritten.

Note: A Message Status Word is written and the pointer is incremented when the BCRTM detects a message error.

C. Data List Pointer. The Data List Pointer is the third word within the descriptor. The BCRTM stores data in RAM beginning

at the address indicated by the Data List Pointer. The Data List Pointer is updated at the end of each successful message with

the next message’s starting address with the following exceptions:

• If the message is erroneous, the Data List Pointer is not updated. The next message overwrites any data

corresponding to the erroneous message.

• Upon receiving a message, if the index is already equal to zero, the Data List Pointer is not incremented and

data from the previous message is overwritten.

D. Reserved. The fourth descriptor word is reserved for future use.

BCRTM-24

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