Communications - Racal Instruments X Series Manual

Communications

1260-100X Theory of Operation B-4
U3 is a programmable logic device (PLD) that handles the
communications between the plug-ins and the Option-01T.
implements the same state machine used in 1260-Series switch
modules. communications proceed as follows.
When the Option-01T is about to write data to a plug-in, it takes
HLBUS_A/D to a logic 1, indicating that the data to be serially
shifted out will be an address. It also drives the HLBUS_R/W
signal low to indicate that data will be written. It then outputs an
8MHz clock on HLBUS_CLK, and places serial data on
HLBUS_DATAIN, synchronous with HLBUS_CLK. The first 13 bits
of data represent the address to be written to, with the most-
significant bit first. This address is relative to the A24 address
offset assigned to the Option-01T by RESMAN.
address 0 references the first address in the space allocated to the
Option-01T.
The 13 address bits are clocked into a shift register internal to U3.
The parallel outputs of this shift register are connected directly to
all six plug-ins via the 1260-100 backplane.
After sending the address, The Option-01T drives HLBUS_A/D
low, indicating that the next data sent will be data. It then shifts the
serial data that will be written to the address just sent. There are
eight data bits, with the most-significant bit sent first.
After the last data bit has been sent, the signal HLBUS_STROBE
transitions to a logic high for one clock period of HLBUS_CLK.
HLBUS_STROBE is sent to the six plug-ins.
containing the addressed device uses HLBUS_STROBE to latch
the data into the device.
To read data from a plug-in, the Option-01T begins by taking
HLBUS_A/D to a logic 1, indicating that the data to be serially
shifted out will be an address. It also drives the HLBUS_R/W
signal high to indicate that data will be read. It then outputs an
8.25 clock on HLBUS_CLK, and shifts the address out on
HLBUS_DATAIN, as it does when writing.
The 13 address bits are clocked into U5 and U6, as when writing.
After sending the address, the Option-01T drives the HLBUS_A/D
low, indicating that it is ready for data. The plug-in containing the
addressed device
HLBUS_DATAOUT.
significant bit sent first.
The signal HLBUS_STROBE is used only when writing, not when
reading. During reading, it remains at logic 0.
1260-100X User Manual
begins shifting
There are eight data bits, with the most-
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It
For example,
The plug-in
serial data onto