Racal Instruments 1260-100, Manual

1260-100/101 Adapt-a-Switch Carrier Module User Manual 

B-7 

LBUSC10S also connects to all other devices controlled by the same Option-01T.  When any 
device in this group asserts a global reset, all devices in the group respond by resetting their 
drivers. 

 Interrupt 

The signal LBUSC11S is an open-collector line to the Option-01T.  It has two purposes.  When a 
plug-in asserts an emergency reset condition, it drives the LBUSC11S signal low.  Also, the 
1260-114 drives the LBUSC11S signal low to announce a synchronous event.  When LBUSC11S 
goes low, the Option-01T polls the plug-ins to determine which one generated the interrupt.  It then 
responds accordingly. 

 Communications 

U1 is a programmable logic device (PLD) that handles the communications between the plug-ins 
and the Option-01T.  It 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.  For example, address 0 references the 
first address in the space allocated to the Option-01T. 

The 13 address bits are clocked into a shift register comprised of U5 and U6.  The parallel outputs 
of this shift register are connected directly to the two plug-ins. 

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 two plug-ins.  The plug-in 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 8MHz 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 begins shifting serial data onto HLBUS_DATAOUT.  There are eight data 
bits, with the most-significant bit sent first. 

The signal HLBUS_STROBE is used only when writing, not when reading.  During reading, it 
remains at logic 0.