MAS281 Dynex, MAS281 Datasheet - Page 10

• Manufacturer Part Number: MAS281
• Description: MIL-STD-1750A Microprocessor
• Manufacturer: Dynex

MAS281
memory fault; bit 5 is set if it goes low during an l/O fault. As
with MPROEN, either condition immediately sets pending
interrupt level 1 and causes the currently executing MIL-STD-
1750A instruction to be aborted .
2.2.35 PROGRAMMED I/O TRANSFER ERROR (PIOXE)
high-to-low transition, is used to inform the module that a
programmed l/O data transfer error has been detected. Bit 6 of
the module Fault Register (FT) is set when this signal goes
low. This, in turn, causes pending interrupt level 1 to be set.
2.2.36 FAULT #7 (FLT7)
high-to-low transition, sets bit 7 of the Fault Register (FT). This
is a user definable fault.
2.2.37 SYSTEM FAULT (SYSF)
high-to-low transition, sets bits 13 and 15 of the Fault Register
(FT). This is a user definable fault.
2.2.38 ILLEGAL ADDRESS (ILLAD)
low or if the bus fault timeout circuit causes an interface
timeout.
2.2.39 MICROCODE STOP (MSTOP)
reserved for use by GEC Plessey Semiconductors. MSTOPN
must be pulled up to VDD in customer applications.
2.2.40 ROM ONLY (ROMONLY)
Semiconductors and must be pulled up to VDD in customer
applications.
3.0 OPERATING MODES
instruction execution, (3) interrupt servicing, (4) fault servicing,
(5) DMA support, (6) Hold support, and (7) timer operations.
3.1 INITIALISATION
response to a hardware reset. This routine clears module
registers, disables and masks interrupts, reads the
configuration register, resets the output discrete register (if
implemented), initialises the MMU and BPU (if implemented),
performs Built-ln-Test (BIT), raises the Start-Up ROM enable
discrete, clears and starts timers A and B, resets the trigger-go
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A low on this active low input, captured by the SYNCN
A low on this active low input, captured by the SYNCN
A low on this active low input, captured by the SYNCN
This active low output drops low if the EXADEN input drops
MSTOPN allows microcode to be single-stepped and is
ROMONLYN is used for testing by GEC Plessey
MAS281 operating modes include: (1) initialisation, (2)
The module executes a microcoded initialisation routine in
counter, and loads the instruction pipeline. Table 2
summarises the resulting initialisation state, and Table 3
provides a detailed breakdown of the initialisation sequence.
begins by pulling NPU low. This is the first time after reset that
NPU is guaranteed low. If all five subroutines execute
successfully, NPU is raised high. If any part of BIT fails, an
error code identifying the failed subroutine is loaded into the
Fault Register (FT), BIT is aborted, and NPU is left in the low
state. Table 4 defines the coding of BIT results in FT. In the
event of such a failure, the resulting module reset state will be
dependent on where in BIT the error occurred and may not be
the same as that shown in Table 2. A BIT failure indication in
FT will set the level 1 interrupt request bit of the Pending
Interrupt (Pl) register. Since initialisation disables and masks
interrupts, this interrupt request will not be asserted .
load the instruction pipeline. Instruction fetches start at
memory location zero and will be from the Start-Up ROM if
implemented. Whether BIT passes or not, the processor will
begin instruction execution at this point.The system start-up
code may include a routine to enable and unmask interrupts in
order to detect and respond to a BIT failure.
and fault inputs must be high for the duration of the
initialisation routine. Also, timers A and B must be clocked
during this interval, i.e., TCLK must be applied.]
The last action performed by the initialisation routine is to
BIT consists of five subroutines, as outlined in table 4, and
[NOTE: To complete initialisation and pass BIT, interrupt
Instruction Counter (IC)
Status Word (EU and MMU) (SW) Zeroed
Fault (FT)
Pending Interrupt (PI)
Mask (MK)
Interrupts
DMA Access
Timer A
Timer B
Trigger-Go Timer
Page Registers
AL, W, E Fields
PPA Field
Write Protect
Global Memory Protect
Table 2: Initialisation State
MAS281
MMU
BPU
Zeroed
Zeroed
Zeroed
Zeroed
Disabled
Disabled
Reset and Started
Reset and Started
Reset and Started
Group 0 Enabled
Zeroed
Logical to Physical
Map
Zeroed
Enabled