MAS281C Ver la hoja de datos (PDF) - Dynex Semiconductor
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MAS281C Datasheet PDF : 55 Pages
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MAS281
Hold state. Again pulling HOLDN will cause the next instruction
to execute. This process may be repeated as long as required.
Raising HOLDN high will resume normal operatlon.
3.7 TIMER OPERATIONS
The MAS281 implements interval timers A and B, a trigger-
go counter, and a bus fault timer. A discussion of each follows:
l/O) of the Fault Register (FT) is set. This sets pending
interrupt level 1 and causes the current bus cycle to be
terminated by forcing SYNCN low. The MIL-STD-1750A
instruction is aborted, and control passes to the level 1
interrupt service routine (if the level 1 interrupt is unmasked).
This feature is disabled by pulling DTON low.
4. SOFTWARE CONSIDERATIONS
3.7.1 TIMERS A AND B
Timer A is clocked by the TCLK input; timer B is clocked by
an internally generated TCLK/10. MIL-STD-1750A requires
TCLK to be a 100-kHz pulse train. If allowed to overflow, timers
A and B will set level 7 and level 9 interrupt requests,
respectively. Timing characteristics of each timer are defined
in Section 5.0. Either timer can be read, loaded, started, and
stopped through the use of internally decoded XIO commands.
These commands are identified in Table 7b in Section 4.0.
By asserting the DTIMERN input, both timers will halt and all
internally decoded XIO commands which would change their
state are disabled (asserting DTIMERN also disables DMA
accesses by driving DMAE low and DMAKN high). Raising
DTIMERN allows the timers to resume counting from their
suspended state and allows timer commands to function
normally (DMA control lines are again allowed to change).
A feature of the MAS281 timers is the choice of disabling,
or not disabling, the interval timers A and B upon execution of
a BPT software instruction when a Console is connected. If full
compliance with MIL-STD-1750 (Notice 1) is desired, the
halting of timers A and B can be accomplished by pulling
DTIMERN low upon execution of a BPT instruction with a
Console connected. Two suggested ways to do this are: (1)
connect HLDAKN to DTIMERN through an AND gate; or (2)
allow the system Console to pull DTIMERN low upon receiving
HLDAKN low. The first option provides a faster response and
is a less complicated method, whereas the second choice
allows the option of halting timers A and B, or not halting them.
[NOTE: As described in Section 2.2, DTIMERN low
suspends the trigger-go timer and disables DMA access
(forces DMAE low and DMAKN high) in addition to halting
timers A and B].
3.7.2 TRIGGER-GO COUNTER
The trigger-go counter is clocked by the TGCLK input.
Timing characteristics for trigger-go counter operation are
defined in Section 6 0. DTIMERN disables and enables
operation in the same manner as with timers A and B.
Whenever the trigger-go counter overflows, TGON drops low
and remains low until the counter is reset via the GO internal
XIO command.
3.7.3 BUS FAULT TIMER
All bus operations are monitored to ensure timely
completion. A hardware timeout circuit is enabled at the start of
each memory and l/O transfer (DSN high-to-low transition) and
is reset upon receipt of the external ready (RDYN) signal.
If this circuit fails to reset within a minimum of one TCLK
period or a maximum of two TCLK periods, either bit 8 (if the
transaction is with memory) or bit 5 (if the transaction is with
The MAS281 implements the full MIL-STD-1750A
instruction set. Table 7a lists the instruction set and provides
performance data for each instruction. Table 7b provides a
summary of the XIO commands which are internally decoded
on the module. Resources available to the software
programmer are depicted in Figure 9. A discussion of data
types, addressing modes and benchmarking considerations
follows.
4.1 DATA TYPES
The MAS281 fully supports 16-bit fixed-point single
precision, 32-bit fixed-point double-precision, 32-bit floating-
point, and 48-bit extended precision floating point data types.
Figure 10 depicts the formats of these data types.
All numerical data is represented in two’s complement
form. Floating-point numbers are represented by a fractional
two’s complement mantissa with an 8-bit two’s complement
exponent. All floating-point operands are expected to be
normalized. If not normalized, the results from an instruction
are not defined.
4.2 ADDRESSING MODES
The MAS281 supports the eight addressing modes
specified in MIL-STD-1750A. These addressing modes are
depicted in Figure 11 and are defined below.
4.2.1 REGISTER DIRECT (R)
The register specified by the instruction contains the
required operand.
4.2.2 MEMORY DIRECT (D,DX)
Memory Direct (without indexing) is an addressing mode in
which the instruction contains the memory address of the
required operand. In Memory Direct-lndexed (DX), the
memory address of the required operand is specified by the
sum of the contents of an index register (RX) and the
instruction address field (A). Register R1 through R15 may be
specified for indexing.
4.2.3 MEMORY INDIRECT (I, IX)
Memory Indirect (without indexing) is an addressing mode
in which the memory address specified by the instruction
contains the address of the required operand. In Memory
Indirect with Pre-lndexing (IX), the sum of the contents of a
specified index register and the instruction address field in the
address that contains the address of the required operand.
Registers R1 through R15 may be specified for pre-indexing.
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