Publication No. 500-001184-000 Rev. B.0
Theory of Operation 13
Figure 1-1 VMIVME-1184 Block Diagram
During Data-Only operations, the board monitors the external circuitry. When the
board
ʹ
s address decoder determines the board is being accessed, it clocks the
inputs into the data registers, effectively taking a snapshot of the external world.
The data is steered to the correct VMEbus data lines, DTACK* is asserted, and the
board re-arms its address decoder for another cycle. These types of transfers are
always available to the user and do not effect the COS or SOE logic.
During Interrupt Cycles, the Interrupt Processor (IP) handles the board’s
functionality. When the COS logic issues an interrupt request to the IP, it also
stores the incoming data in the associated FIFOs. The IP issues an interrupt
request to the host CPU and waits for the proper Interrupt Acknowledge cycle.
When the IP responds to the Acknowledge cycle, it places the user-programmed
vector for the Interrupt Service Routine (ISR) on the VMEbus.
1.2 VMEbus Interface
The bus interface logic consists of bus signal buffers and transceivers that meet
the VMEbus specification loading requirements. The address decoder (or board-
select logic) can respond to standard (24-bit) or short (16-bit) data I/O accesses.
The steering logic selects which VMEbus data lines to connect to the board
ʹ
s
Internal Data Bus (IDB) and which direction the data will flow. The Board
Identification (BD ID) register, the Control and Status Register (CSR) and the COS
Select registers are considered part of the bus interface logic.
7
21
3
4
27
15
32
7
15
3
8
32
32
IDB
32
32
32
P2
Front
Panel
32-Bit
Counter
Board
Address
Selection
Address
Decode
Control
Logic
Data
Transceivers
Interrupt
Processor (IP)
COS
FIFOs
Debounce
Clock
COS
Detection
RS-422
Xcvr
Read Data
Registers
Input
Circuitry
VMEb
us
32 User
Input Pairs
64
6
6
3 Differential Pairs
3 Differential Pairs
FPGA
Quadrature
Counter
Recovery
Opto
Isolation
Op
Amps
32
Front Panel
Status LEDs
64
(+) side used for
Single-Ended
Send/Receive
Broken
Wire
Detection
1
3
32
32
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