GE VMIVME-5576 Fiber-Optic Reflective Memory with Interrupts

this mode of operation, the first of the two transfers is used

unless an error is detected in which case the second transfer

is used. In the event that an error is detected in both transfers,

the node removes the transfer from the system. The

probability of both transfers containing an error is 10-20. or

about one error every 372.000 years at maximum data rate.

PROTECTION AGAINST LOST DATA — Data

received by the node from the fiber-optic cable is error

checked and placed in a receive FIFO.  Arbitration with

accesses from the VMEbus then takes place and the data is

written to the node’s SRAM and to the node’s transmit FIFO.

Data written to the board from the VMEbus is placed directly

into SRAM and into the transmit FIFO.  Data in the transmit

FIFO is transmitted by the node over the fiber-optic cable to

the next node.  Data could be lost if either FIFO were allowed

to become full.

The product is designed to prevent either FIFO becoming

full and overflowing. It is important to note the only way that

data can start to accumulate in FIFOs is for data to enter the

node at a rate greater than 6.2 or 3.2 Mbyte/s in redundant

mode. Since data can enter from the fiber and from the

VMEbus, it is possible to exceed these rates. If the transmit

FIFO becomes half-full, a bit in the Status Register is set and,

if armed, an interrupt is generated. This condition is an

indication to the software in the node that writes to the

Reflective Memory should be suspended until the FIFO

becomes less than half-full. If the half-full indication is

ignored and the transmit FIFO becomes full, then writes to the

Reflective Memory will be acknowledged with a bus error.

With VMEbus writes being blocked by the bus error, data

cannot overflow in the receive FIFO.

NETWORK MONITOR — There is a bit in a Status

Register that can be used to verify that data is traversing the

ring (that is, the ring is not broken). This can also be used to

measure network latency.

SPECIFICATIONS

Memory Size: 256 Kbyte, 512 Kbyte, or 1 Mbyte

Access Time:

400 ns (worst-case arbitration)

200 ns (best-case arbitration)

TRANSFER SPECIFICATION

Transfer Rate:

6.2 Mbyte/s (longword accesses) without redundant

transfer

3.2 Mbyte/s (longword accesses) with redundant transfer

COMPATIBILITY

VMEbus: This product complies with the VMEbus

specification (ANSI/IEEE STD 1014-1987. IEC 821 and

297), with the following mnemonics:

A32: A24: D32/D16/D08 (EO): Slave: 39/3D:09/0D

Form factor: 6U

Memory: Addressable on 256 Kbyte boundaries for

256 Kbyte memory option

Addressable on 512 Kbyte boundaries for 512 Kbyte

memory option

Addressable on 1 Mbyte boundary for 1 Mbyte memory

option

INTERCONNECTION

Cable Requirements: Two fiber-optic cables

Cable Length: 2.000 m maximum between nodes

Configuration: Daisy chain ring up to 256 nodes

PHYSICAL/ENVIRONMENTAL

Temperature Range: 0 to 55 °C, operating-40 to 85 °C, storage

Relative Humidity: 20 to 80 percent, noncondensing

Power Requirements: 5.0 A maximum at +5 VDC

MTBF: 142.400 hours (217F)

DATA TRANSFERS

Data written into the Reflective Memory is broadcast to

all nodes on the network without further involvement of the

sending or receiving nodes.  Data is transferred from memory

locations on the sending nodes to corresponding memory

locations on the receiving nodes.

A functional block diagram of the VMIVME-5576 is

shown in Figure 1.

TRADEMARKS

The VMIC logo is a registered trademark of VMIC.

Other registered trademarks are the property of their

respective owners.