MA17501
MA17501
Radiation Hard MIL-STD-1750A Execution unit
Replaces March 1997 version, DS4548 - 2.3
DS4548 - 3.2 January 2000
The MA17501 Execution Unit is a component of the Dynex
Semiconductor MAS281 chip set. Other chips in the set
include the MA17502 Control Unit and the MA17503 lnterrupt
Unit. Also available is the peripheral MA31751 Memory
Management Unit/Block Protection Unit. These chips in
conjunction implement the full MlL-STD-1750A lnstruction Set.
The MA17501 - consisting of a full function 16-bit ALU, 24 x
16-bit dual-port RAM register file, 32-bit barrel shifter, 4 x 24-
bit parallel multiplier, synchronisation clock generation logic,
and microcode decode logic - provides all computational,
logical, and synchronisation functions for the chip set. Table 1
provides brief signal definitions.
The MA17501 is offered in several package styles
including; dual-in-line, flatpack and leadless chip carrier. Full
packaging information is given at the end of the document.
BLOCK DIAGRAM
FEATURES
s
MIL-STD-1750A Instruction Set Architecture
s
Full Performance over Military Temperature Range
(-55°C to +125°C)
s
Radiation Hard CMOS/SOS Technology
s
16-Bit Bidirectional Address/Data Bus
s
16-Bit Full Function Registered ALU
s
32-Bit Barrel Shifter
s
24 x 16-Bit Dual-Port RAM File
• 16 User Accessible General Purpose Registers
• 8 Microcode Accessible Registers
s
4 x 24-Bit Parallel Multiplier
• 48-Bit Accumulator
• 16-Bit x 16-Bit Multiply in 4 Machine Cycles
s
Instruction Pre-Fetch
s
MAS281 Integrated Built-in Self Test
s
TTL Compatible System Interface
1.0 SYSTEM CONSIDERATIONS
The MA17501 Execution Unit (EU) is a component of the
Dynex Semiconductor MAS281 chip set. This chip set
implements the full MlL-STD-1750A instruction set
architecture. The other chips in the set are the MA17502
Control Unit (CU) and the MA17503 Interrupt Unit (IU). Also
available is the peripheral MA31751 Memory Management
Unit/Block Protection Unit (MMU(BPU)).
Figure 1 depicts the relationship between the chip set
components. The EU provides the arithmetic and logical
computation resources for the chip set. The EU also provides
program sequencing logic in support of branching and
subroutine functions. The lU provides interrupt and fault
handling resources, DMA interface control signals, and the
three MIL-STD-1750A timers. The EU and lU are each
controlled by microcode from the CU. The MMU(BPU) may be
configured to provide 1M-word memory management (MMU)
and/or 1K-word memory block write protection (BPU)
functions.
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MA17501
Figure 1: MAS281 Chip Set with Optional MA17504 and Support RAMs
As shown in Figure 1, the MAS281 is the minimum
processor configuration consisting of an Execution Unit, a
Control Unit, and an Interrupt Unit. This configuration is
capable of accessing a 64K-word address space. Addition of a
MA31751 allows access to a 1M-word address space and/or
provides hardware support for 1K-word memory block write
protection.
The EU, as with all components of the MAS281 chip set, is
fabricated with GEC Plessey Semiconductors CMOS/SOS
process technology. lnput and output buffers associated with
signals external to the MAS281 are TTL compatible.
Detailed descriptions of the EU's companion chips are
provided in separate data sheets. Additional discussions on
chip set system considerations, interconnection details, and
DAlS mix benchmarking analysis are provided in separate
applications notes.
The Execution Unit consists of a full function 16-bit ALU,
32-bit barrel shifter, 4 x 24-bit parallel multiplier, 24 x 16bit
dual-port RAM register file, processor status word register,
three operand transfer registers, three instruction fetch
registers, various interconnect buses, synchronization clock
generation logic, and microcode decode logic. Details of these
components are depicted in Figure 2 and are discussed below:
2.0 ARCHITECTURE
2.1 ALU
The ALU is a full function 16-bit arithmetic/logic unit
capable of performing arithmetic and logic operations on either
one or two 16-bit operands in a single machine cycle. ln
addition to operand manipulation, the ALU is used to compute
memory addresses.
The ALU supports 16-bit fixed-point single-precision, 32-bit
fixed-point double-precision, 32-bit floating-point, and 48-bit
floating-point extended-precision data in two’s complement
representation. Double-precision and extended-precision
operands are passed through the ALU 16 bits at a time on
consecutive machine cycles. Machine flags provide an
indication of ALU results and are used to set condition status
(CS) bits C, P, Z, and N in the Status Word Register. Condition
status bits and the Status Word register are discussed below.
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MA17501
Signal
AD00 - AD15
AS
CLKPC
CLK02
PAUSE
DS
HLDAK
HOLD
lN/OP
INTRE
lRDY
M/lO
M00 - M19
OSC
OVl
PlF
RD/W
RDY
RESET
SYNCLK
SYNC
SYSCLK1
TEST
T1
VDD
GND
I/O
I/O
O/Z
O
O
l
O/Z
O
l
O/Z
O
l
O/Z
l
l
O
l
O/Z
l
l
O
O
O
I
O
Definition
External 16-Bit Address/Data Bus
Address Strobe Indicates Address lnformation on A/D Bus
Precharge Clock
Phase 2 Clock
DMA Acknowledge (A/D Bus to be used for DMA)
Data Strobe lndicates Data lnformation on A/D Bus
Hold Acknowledge
Hold Request Suspends lnternal Processor Functions
lnstruction/Operand lndicates Type of Memory Access
lnterrupt Enable
lnterrupt Unit Ready Signal
Memory or lnput/Output lndicates Transaction on A/D Bus
20-Bit Microcode Bus
External Oscillator Clock
Overflow lndicator
Privileged Instruction Fault
Read/Write IndicatesData Direction on A/D Bus
Ready lnforms CPU of the Conclusion of External Bus Cycle
Reset Indicates Device Initialization
Interrupt Unit's Sync Clock
System Clock - CPU Sync Clock (External)
System Clock (Internal)
Test Enable
Branch or Jump Control
Power (External), 5 Volts
Ground
Table 1: Signal Definitions
2.2 BARREL SHIFTER
The Barrel Shifter is a 32-bit input, 16-bit output right shift
network. A 32-bit operand may be shifted right arithmetically,
logically, or cyclically up to 31 bit positions in a single machine
cycle. While not directly accessible or visible to user programs,
the Barrel Shifter is utilized by microcode to effect all shift,
rotate, and normalize instructions with minimum execution
time.
2.3 PARALLEL MULTIPLIER
The Parallel Multiplier performs a 4-bit multiplier by 24-bit
multiplicand multiplication plus accumulation in a single
machine cycle. Only four machine cycles are required to
complete a 16-bit by 16-bit multiplication. Contained within the
multiplier is a 48-bit product accumulation register with the
lower 24 bits serving as a source operand register.
On each multiply machine cycle, the lower four bits of the
accumulator are multiplied by 24 bits from the two ALU
operand source buses (R and S). The lower 24 bits of this 28-
bit product are then added to the upper 24 bits of the
accumulator and the whole accumulator is shifted right four
bits. This right shift makes room for the upper four bits of the
product. The four bits shifted out are used in the next multiply
iteration.
2.4 DUAL-PORT REGISTER FILE
The Register File is a dual port RAM structure containing
24, 16-bit registers. Sixteen of these registers are general
purpose and user accessible. These user accessible registers
- referred to as R0 through R15 - may be used as
accumulators, index registers, base registers temporary
operand registers, or stack pointers. The remaining eight
registers are only accessible by microcode.
Adjacent registers are concatenated to effectively form 32-
bit and 48-bit registers for storage of double precision and
extended-precision operands, respectively. Instructions
access these operands by specifying the register containing
the most significant part of the operand, and the register set
wraps around automatically under microcode control, e.g.,
R15 concatenates with R0 for 32-bit operands and R15
concatenates with R0 and R1 for 48-bit operands.
3/35
MA17501
Figure 2: MA17501 Execution Unit Architecture
2.5 STATUS WORD REGISTER
The Status Word Register (SW) holds the condition status
(CS) bits C, P, Z, and N generated by ALU operations. The SW
also stores the address state (AS) and processor state (PS)
fields. Figure 3 defines the Status Word Register storage
format. The CS bits are stored with each logical, shift, and
arithmetic operation performed by the ALU as required by MlL-
STD-1750A and remain valid until changed by subsequent
operations. The CS bits are interrogated during "jump on
condition" and "instruction counter relative" MlL-STD-1750A
branch instructions.
2.6 OPERAND TRANSFER REGISTERS
The Address (A), Data Output (DO), and Data lnput (Dl)
registers are referred to as Operand Transfer Registers. These
registers serve as storage buffers between internal EU buses
and the EU's externally accessible address/data (AD) Bus.
The DO register buffers data transferred from the EU to the AD
Bus. The A register buffers operand addresses and XlO
commands onto the AD Bus. The Dl register buffers data
transferred from the AD Bus to the EU .
4/35
MA17501
A 20-bit multiplexed microcode (M) bus provides a
pathway between the Control Unit (CU) and the Execution
Register (E) buffered microcode decode logic on the EU chip.
Microcode placed on this bus by the CU controls all actions of
the EU.
2.9 SYNCHRONISATION CLOCK GENERATION LOGIC
The Execution Unit generates all of the synchronisation
clocks required by the chip set and CPU system. The EU
converts an externally supplied oscillator signal into five
synchronisation signals: SYNCN, SYSCLK1N,SYNCLKN,
CLKPCN, CLK02N. The EU generates SYNCN for elements
external to the chip set whereas SYNCLKN and SYSCLK1N
are generated for the Interrupt Unit and internal EU
synchronisation, respectively. SYSCLK1N is also brought out
on a pin for use by external monitoring systems. The EU
generates CLKPCN and CLK02N for use in the Control Unit.
The CU uses CLKPCN to precharge the M Bus and transmit
the first microword while CLK02N is used to transmit
microword two.
The EU also contains the wait state generation interface.
Failure of memory or l/O subsystems to drive RDYN low at the
proper time during the DSN pulse causes the EU to hold
SYNCLKN, SYNCN, SYSCLK1N, and CLKPCN in the high
state; CLK02N, AS and DSN, in the low state; and RD/WN, IN/
OPN and M/ION in their current states for one or more
oscillator cycles beyond the end of the normal five OSC cycle
machine cycle. When RDYN is asserted low, the EU allows the
machine cycle to conclude at the high-to-low transition of the
current oscillator cycle. This will allow all the synchronisation
and control signals to resume normal operation.
Additionally, IRDYN is used to signal completion of internal
l/O command control of the lnterrupt Unit (IU). The IU thus can
extend the duration of the above mentioned bus signals.
Failure of the lU to drive lRDYN low at the proper time during
the DSN low pulse causes the EU to hold SYNCLKN, SYNCN,
SYSCLK1N, and CLKPCN in the high state; CLK02N, AS, and
DSN in the low state; and lN/OPN, M/lON, and RD/WN in the
state for the normal five OSC cycle machine cycle. When the
lU asserts IRDYN low, the EU allows the machine cycle to
conclude at the high-to-low transition of the current oscillator
cycle. This will allow all the synchronisation and control signals
to resume normal operation.
[NOTE: Whenever the EU is executing a machine cycle
which requires IRDYN to drop low for completion, the machine
cycle will be a minimum of six OSC cycles long. The maximum
duration of this machine cycle depends on the length of time
that the lU holds IRDYN high.]
Figure 3: Status Word Format
2.7 INSTRUCTION FETCH REGISTERS
The Instruction Counter (IC), Instruction A (IA), and
Instruction B (IB) registers allow sequential instruction fetches
to be performed without assistance from the ALU. The lC
register, which holds the 16-bit address of the next instruction
to be fetched from memory, is loaded automatically by reset,
jump, or branch operations. Once loaded, it functions as a
dedicated counter to sequence from one instruction to the
next. The current IC contents may be stored in registers R0
through R15 or in memory (pushed onto a stack) to provide
return linkages for subroutine calls. As part of the microcoded
interrupt handling routine the lC is saved in memory via the
interrupt linkage pointer.
Registers lA and IB provide an instruction look-ahead
capability. ln the case of 16-bit instructions, lB holds the
instruction currently executing while lA holds the next
instruction to be executed. ln the case of 32-bit instructions, IB
and lA each hold half of the instruction. IA and Dl (Dl stores the
immediate operands) are loaded as the instruction in lA is
transferred to lB for execution; if the instruction in lB uses an
immediate operand, lA is reloaded with the next instruction
while Dl maintains the immediate data. This overlapping of
operations allows higher performance levels to be achieved.
2.8 BUSES
Three 16-bit wide buses (R, S, and Y) interconnect the EU
data storage and computational elements. The R and S buses
accept operands from selected EU data storage elements and
route them to inputs of selected EU computational elements.
The Y, or destination, bus serves to route computational
results either back to EU data storage and computational
elements or to the various operand transfer registers.
A 16-bit multiplexed Address/Data (AD) Bus provides a
communications path between the EU, other components of
the MAS281 chip set, and any other devices mapped into the
chip set's address space. Data transfers between the AD Bus
and the R, S, and Y buses are buffered by the operand transfer
registers.
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