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*ACC Micro...
**ACC2087 Enhanced Super Chip (486 Single Chip) <Aug96
***Info:
[no general description]
[below is *selected* parts of the functional description]
The ACC2087 supports the 486 and 386DX CPUs. The CPU interface
selection is determined by detecting a pull up or pull down resistor
on pin 172 (M486) during the reset period. A pull up resistor on pin
172 will trigger the ACC2087 operating in the 486 mode. A pull down
resistor on pin 172 will trigger the ACC2087 operating in the 386DX
mode.
80387 Interface Control:
The 80387 interfaces directly to the 386DX with the error-reporting
logic built in the ACC2087. A coprocessor error is sent to the
ACC2087, generating an interrupt request to the CPU, followed by a
service request. A write operation to I/O port 0F0 will clear the
interrupt request.
Clock Throttling:
To further reduce the power consumption in the Notebook system, the
ACC2087 supports another mode called Clock Throttling. After scaling
the CPU clock, the ACC2087 can periodically assert the STPCLK# request
which will force the CPU into Stop Grant State. Hence the CPU power
can be further reduced.
Local Bus Peripheral Support Master / DMA Mode and SMM Support in
Local Bus Cycle:
The ACC2087 supports VL-Bus with master and DMA modes. To further
enhance the flexibility, the local bus can be detected under System
Management Mode (SMM).
Intel System Management Mode Interface (SMM)
System Management Mode (SMM) is designed to handle power management
interrupts that are totally transparent to the existing programs,
operating systems and CPU operation modes. The ACC2087 contains
dedicated logic to interface with SMM implemented by the Intel
SL-enhanced 486 for battery-powered portable computers. The ACC2087
utilizes the DRAMs located between segments A000h and B000h as the
separate SMM memory (SMRAM) required by SMM functions.
Power Management Features:
The ACC2087 provides a powerful mechanism of system power management
that is completely transparent to the operating system and application
software. It was designed from the system level to synthesize and
manage power consumption for the lowest power operation while
maintaining system performance in the portable system.
High Performance Cache Controller:
The integrated ACC2087 cache controller supports a direct mapped cache
from 32 Kbytes up to 2 Mbytes in size. The direct mapped architecture
means that a specified line in the cache is capable of caching only a
certain range of memory addresses. The low order address bits choose
the location (index) while the high order address bits (tag) identify
the entry.
As for write policy, the ACC2087 supports either write through or
write back cache implementations. In addition, the ACC2087 cache
architecture can be used in both 386DX and 486 applications. For a
386DX design, the ACC2087 cache controller can be used to support a
primary cache. In a 486 AT system, if the internal cache of the 486 is
enabled, the ACC2087 direct mapped cache can be used as secondary
cache.
Memory Controller:
The Memory Controller is a key feature of the ACC2087. This versatile
circuit provides complete control of up to 64 megabytes of system
DRAM. In any control mode, it generates up to four Row Address Strobes
(RAS#0-3) and one Memory Write Enable signal (WEN#). The Memory
Controller also provides the interface to transfer control to a DMA
controller or an AT Bus master.
The ACC2087 Memory Controller supports 256KB, 512KB, 1MB and 4MB DRAM
devices. The ACC2087 provides all control signals and programmable
control to support 256Kx1, 512Kx1, 1Mx1, 1Mx4, 4Mx1 and 4Mx4
(symmetrical only).
Memory Mapping:
Memory Mapping translates system RAM within the 640 KB to 1MB range,
which is reserved for the system ROM and BIOS application, to an
accessible address range above the physical RAM space. For example, if
4 MB of memory are installed, and the memory mapping feature is on,
the DRAMs in the 640 KB to 1MB range are mapped to an address
immediately above 4 MB.
Shadow RAM
Shadow RAM provides an option to transfer BIOS or video-extension BIOS
program codes into system RAM. This option provides significant
performance improvement for applications requiring intensive BIOS
calls.
Shadow RAM implements an alternate BIOS source by copying the complete
EPROM program code into system RAM. This is referred to as "shadowing"
because the DRAM and EPROM are both located in the same physical
address space. This change is transparent to the rest of the
system. ROM can then be disabled, allowing the RAM to respond in its
place.
Interrupt Controllers
There are two programmable interrupt controllers for the ACC2087. They
are fully compatible with Intel's 8259 controller, providing up to 15
interrupt sources (14 external and 1 internal). The internal line
connects to the 8254 Counter 0 output.
These interrupt controllers prioritize interrupt requests to the CPU.
DMA
The ACC2087 has two DMA controllers, compatible with the Intel 8237,
which provide a total of seven external DMA channels.
Combined with the Memory Mapper, each DMA channel has a 24-bit address
output to access data throughout the 64 megabyte system address space.
Memory Mapper
The ACC2087 has a built-in logic equivalent to the 74LS612, generating
the upper address bits during a DMA cycle.
Timer/Counter
The ACC2087 provides three internal counters, which are compatible
with the 8254. The clock input for each counter is tied to a clock of
1.19 MHz, which is derived by dividing the 14.318 MHz crystal input by
12. The output of Counter 0 is connected to the IRQ0 input of
interrupt controller 1. Counter 1 initiates a refresh cycle and
Counter 2 generates sound waveforms for the speaker.
ACC2087 I/O Address Map
The ACC2087 I/O address decode is fully compatible to the IBM PC/AT
requirements. The ACC2087 has decoded the I/O address range from 000
to 0FF to allow users to use the I/O areas not used by the IBM PC/AT.
PIO
The PIO is the system configuration to control the speaker port. It
also has circuitry to detect refresh. This condition can be read back
as Bit 4 of I/O Port 61h.
DMA Arbitration Logic
There are two possible sources for a hold request to the CPU. Either
the DMA controller issues a hold request or the output of Counter 1 in
the 8254 makes a low to high transition. The HOLD line is active when
either source is requesting a hold. The ACC2087 contains the logic to
do the arbitration.
Refresh Generation Logic
The ACC2087 contains circuitry to perform DRAM refresh cycle. Refresh
circuitry contains an 8-bit counter for address SA0-7 during a
refresh. In addition, three more address counter bits are presented
inside the ACC2087 to support refresh for DRAMs up to 4M bits.
Staggered Refresh Logic
The ACC2087 refresh logic works to perform a periodic refresh for both
system DRAM and extended RAM on the AT Bus. The ACC2087 initiates a
refresh cycle by driving its REFRESH# output low, and driving the
refresh address onto the MA Bus, simultaneously generating staggered
refresh pulses on the four RAS outputs. The RAS outputs are staggered
to reduce the current drain caused by the refresh operation. During
each refresh cycle, the ACC2087 drives the current refresh address
onto the AT address bus. This provides the refresh address for
extended memory.
NMI and Port B Logic
The ACC2087 contains non-maskable interrupt (NMI) signal generation
logic. An NMI can be caused by an I/O error or by a parity error. Port
B identifies the source of the error. At power up, the NMI signal is
masked off. NMI is enabled by writing to I/O address 070 with bit 7
low; NMI is disabled by writing to I/O address 070 with bit 7 high.
Bus Controller and Converter
The flexible ACC2087 Bus Controller provides all of the control logic
needed to interface to the CPU, alternate masters, local memory,
primary or secondary cache and the AT bus. Each access may be
initiated by the ACC2087 decoding the address and cycle type provided
on the local CPU bus. The cycle type is determined by monitoring the
signals D/-C, W/-R and M/-IO.
Turbo Speed Control Logic
The CPU clock frequency can be switched between CLKSRC and the AT
clock. The frequency switch can be generated through either hardware
or software. A TURBO pin is provided to support a front panel turbo
speed switch. TURBO high selects CLKSRC as the CPU clock. TURBO low
selects AT Bus clock as the CPU clock.
For power conservation, a standby mode clock control is provided. A
system needs to pre-select the standby frequency first, then BIOS will
monitor the activity of the system. If all pre-defined conditions of
the standby mode are satisfied, the system will go into the standby
mode by programming bit 3 of Register 8h to 1 or if the Turbo/Sleep
bit has been set to 1. The Turbo pin, when driven low, will force the
system into sleep mode.
OS/2 Optimization
The ACC2087 implements OS/2 optimization, which is a more efficient
way to switch back and forth between real and protected modes in an
OS/2 environment when frequent DOS calls are made. Conventional
methods require the processor to communicate with the integrated
/external keyboard controller in switching to protected mode and
activating gate A20.
With OS/2 optimization, the ACC2087 allows control of software CPU
reset and A20 gating through Port 92h.
Floppy Disk Drives
With the ACC2087, designers can build an IBM PC/XT or AT compatible
Floppy Disk Drive with fast access time, high reliability and low cost
per bit capability. The ACC2087 integrates the functions of a standard
floppy disk drive controller.
Data separator
Write precompensation circuit
Decode logic
Data rate selection
Clock generation
Drive interface drivers and receivers.
This integration greatly reduces the number of components required to
interface floppy disk drives to a microprocessor system.
Serial Port Interface
The ACC2087 supports two NS16C550 compatible serial ports. Each serial
port interface converts data from peripheral devices or modems from
serial-in-data to parallel-out-data. Data transmitted from the CPU is
converted from parallel-in-data to serial-out-data. The status of the
UART can be read during any CPU operation. Status includes type and
condition of the transfer operations in progress, and error
conditions.
Parallel Port Interface
The parallel port interface in the ACC2087 provides compatibility for
a Centronics type printer. Its configuration register allows the
parallel port to be configured in PS/2 type bi-directional parallel
port and Extended Capabilities Port (ECP) modes.
***Configurations:...
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**
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