22
Data Device Corporation
www.ddc-web.com
BU-61559 Series
C-12/02-300
PROCESSOR INTERFACE TIMING
FIGURES 22 and 23 illustrate the timing for the host processor
to access the BU-61559's internal RAM in buffered mode. FIG-
URE 22 illustrates the buffered read cycle timing, while FIGURE
23 shows the buffered mode write cycle.
During a CPU transfer cycle, STRBD and SELECT must be sam-
pled low for two consecutive clock cycles when the BU-61559 is
not
accessing the shared RAM. At this time, the output signals
IOEN and MEMENA-OUT are asserted low. IOEN is used to
enable external address and data tri-state buffers, if required.
MEMENA-IN is the Chip Select (CS) input to the BU-61559's
internal RAM. In the buffered mode, MEMENA-OUT must be
connected directly to MEMENA-IN. In the transparent mode, an
external address decoder may be used to provide MEMENA-IN,
as shown in FIGURE 20.
For a read cycle in the transparent mode, the output signal
MEMOE is asserted low one-half clock cycle after IOEN goes
low. MEMOE will remain low until the end of the read transfer
cycle. For a CPU write cycle in transparent mode, the output sig-
nal MEMWR is asserted low for one clock cycle (62.5 ns nomi-
nal), starting one clock cycle after IOEN is asserted low.
Three clock cycles (nominally 187.5 ns) after IOEN goes low, the
BU-61559 will assert the handshake output READYD low. This
informs the host processor that read data is available on D15-D0
or that write data has been stored. At this time, the CPU should
bring SELECT and STRBD high, completing the transfer cycle.
With two exceptions, the BU-61559 processor interface opera-
tion for accessing registers and internal RAM is essentially the
same for both the buffered and transparent interface modes.One
difference is the operation of the address latch/buffers, as
is that for CPU accesses to external RAM in the transparent
mode, the data buffers remain in their high impedance state.
HARDWARE RESET (MSTCLR)
The MSTCLR control input to the BU-61559 provides a hardware
reset capability. A negative pulse of 50 ns or more will reset all
internal logic of the AIM-HY'er hybrid to its power turn-on or reset
idle state. In most systems, MSTCLR is connected to the host
processor's power turn-on RESET circuit.
BU-61559 INTERFACE TO STANAG 3910 HIGH-
SPEED PROTOCOL CHIP
STANAG 3910 HIGH-SPEED PROTOCOL CHIP
The 1553 BC/RT/MT is comprised of the DDC BU-61559 hybrid
and the two BUS-25679 transformers. In this interface, the BU-
61559 is configured in the transparent mode, interfacing to the
host processor by means of external data and address buffers.
This allows a STANAG 3910 High Speed Protocol Chip to moni-
tor all 1553 words being transferred over the BU-61559's paral-
lel data bus, D15-D00.
The STANAG 3910 remote terminal is comprised of a high-
speed RT protocol chip, data retiming unit, a 20 MHz fiber optic
transceiver, and RAM for high-speed messages. In some imple-
mentations, the data retiming unit and fiber optic transceiver may
be one component.
In general, The High Speed Protocol Chip operates by monitor-
ing the data bus, as well as various control signal outputs from
the BU-61559. The BU-61559 control signals that may be moni-
tored
include
BCSTRCV,
RXDTA_STR, TXDTA_STR, and MEMENA-OUT. The High
Speed Protocol Chip provides the MEMENA-IN input to the BU-
61559.
MSG_ERROR,
CMD_STR,
In the transparent interface mode, Command Words and High-
Speed Action Words may be monitored on the BU-61559's exter-
nal address and data buses.The High Speed Protocol Chip per-
forms all high-speed protocol operations, transmitting and
receiving messages over the 3910 fiber optic bus by means of
the data retiming unit and fiber optic transceiver.
When the BU-61559 receives a transmit command to the High-
Speed subaddress, the High Speed Protocol Chip captures the
Command Word.The High Speed Protocol Chip is then enabled
by the BU-61559's MEMENA-OUT and TXDTA_STR outputs to
provide the High-Speed Status, BIT, and Last Action words over
the BU-61559's data bus. When it does this, the High Speed
Protocol Chip presents the MEMENA-IN input to the BU-61559
high, de-selecting the BU-61559's internal (or possibly external)
RAM. The BU-61559 then responds over the 1553 (3838) bus
with the Data Words provided by the High Speed Protocol Chip.