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**82495XP/490XP Cache Controller / Cache RAM (for i860)       06/05/91
***Notes:...
***Info:...
***Features:...
**82496/491     Cache Controller / Cache RAM (for P5 Pentium) 03/22/93...
**82497/492   Cache Controller / Cache RAM (for P54 Pentium)    <Nov94...
**82498/493   Cache Controller / Cache RAM (for P54 Pentium)    <Nov94...
**
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**SL82C465    Cache Controller (for 486/386DX/SX)                 c:91
***Info:
The SL82C465 cache controller supports both 1X and 2X clock modes. The
1X clock  mode means that the CCLK2  signal is used as  the CPU clock;
the 2X clock  mode means that the PCLK signal  (half the frequency and
the phase indicator  of CCLK2) is used as the  CPU clock. The SL82C465
and other CPU local bus devices run at the same clock frequency as the
CPU, while  the rest of the system  runs at the frequency  of PCLK. In
other words, the operating frequency of the system logic is either the
same (2X clock mode) or half the speed of the CPU (1X clock mode). For
the 1X clock mode, the timing of the signals between the CPU/Cache and
the system logic interface  is converted by the SL82C465 automatically
to  satisfy  the requirement  of  individual  clocks.  Table 1-1  [see
datasheet] lists  the operating frequencies  of the CPU local  bus and
the system logic with the oscillator used.

The 2X  clock mode is recommended  for a CPU frequency  no faster than
33Mhz because the system logic  is available at the targeted speed and
the  performance  is  slightly  better  than if  1X  clock  mode  were
used. For  a CPU  frequency faster  than 33Mhz, the  1X clock  mode is
preferred  for  486  systems  because  it  becomes  increasingly  more
difficult to  build a reliable  system with an oscillator  faster than
66Mhz.

***Versions:...
***Features:...
*TI (Texas Instruments)...
**SN74LS610/2 IBM AT: SN74LS610, SN74LS612 Memory Mappers          <84
***Notes:...
***Info:
Each 'LS610  and 'LS612  memory mapper  integrated circuit  contains a
4-line to  16-line decoder, a  16-word by  12-bit RAM, 16  channels of
2-line to 1-line multiplexers, and  other miscellaneous circuitry on a
monolithic chip. Each  'LS610 also contains 12 latches  with an enable
control.

The memory  mappers are designed  to expand a  microprocessor's memory
addressing capability by  eight bits. Four bits of  the memory address
bus (see  System Block Diagram)[see  datasheet] can be used  to select
one of 16 map registers that contain  12 bits each.  these 12 bits are
presented  to the  system memory  address bus  through the  map output
buffers  along with  the  unused  memory address  bits  from the  CPU.
However, addressable memory space  without reloading the map registers
is the  same as would  be available with  the memory mapper  left out.
The  addressable  memory  space  is  increased  only  by  periodically
reloading the  map registers  from the  data bus.   This configuration
lends itself  to memory utilization  of 16 pages of  2^(n-4) registers
each  without reloading  (n -  number of  address bits  available from
CPU).

These  devices have  four modes  of operation:  read, write,  map, and
pass.  Data may be read from  or loaded into the map register selected
by  the register select  inputs (RS0  thru RS3)  under control  of R/W
whenever chip select (CS) is low. The data I/O takes place on the data
bus DO thru D7. The map  operation will output the contents of the map
register selected by the map address  inputs (MA0 thru MA3) when CS is
high and  MM (map mode control)  is low. The 'LS612  output stages are
transparent in this mode, while  the 'LS610 outputs may be transparent
or latched. When CS and MM are both high (pass mode), the address bits
on MA0 thru MA3 appear at M08-MO11, respectively (assuming appropriate
latch control) with  low levels in the other bit  positions on the map
outputs.
***Versions:...
***Features:...
**TACT82000   3-Chip 286 [no datasheet]                            c89...
**TACT82411   Snake  Single-Chip AT Controller                     c90...
**TACT82S411  Snake+ Single-Chip AT Controller [no datasheet]      c91...
**TACT83000   AT 'Tiger' Chip Set (386)                            c89...
**TACT84500   AT Chip Set (486, EISA) [no datasheet, some info]    c91...
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