Specifications

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2.3 ONBOARD DEVICE OPTIONS AND CONFIGURATION
This section includes the configuration and installation of onboard devices and options. These
include DRAM and byte-wide memory devices, nonvolatile RAM cartridges, math coprocessor,
and a variety of onboard expansion MiniModules including the Ampro MiniModule video
controllers.
2.3.1 CPU and Bus Half-Speed Options
The speed of the CPU or of the AT Expansion Bus can be switched to one-half of the normal
clock speed under software control. This is set using the Ampro SETUP or SETSPEED
utilities, as described in Chapter 3.
When the CPU speed is set to "half-speed," then the AT Expansion Bus speed will also run at
half-speed, since it cannot exceed that of the CPU. In addition, it should be noted that the DMA
controller runs at one-half of the CPU rate, so its speed is linked to the setting of the CPU half-
speed option, not the bus half-speed option.
Reducing the CPU speed can be useful in lowering system power consumption for battery
powered applications, or in increasing the system operating temperature range by reducing the
amount of heat generated by key system components such as the DRAM memory.
Operation of the AT Expansion Bus at half speed may be required to allow the use of plug-in
cards which were designed to be used in older PC compatible systems with lower system clock
rate, or to permit the use of longer bus expansion cables.
The initial state of the CPU and bus half-speed options is determined by parameters stored in the
nonvolatile Configuration Memory, which you can set using the Ampro SETUP utility. During
system operation, the values of CPU and bus half-speed options can be altered dynamically as
desired, using the Ampro SETSPEED utility. Refer to the information on the use of the SETUP
and SETSPEED utilities in Chapter 3 and Appendix A for details.
2.3.2 DRAM Memory
The board has positions for up to four s ingle i n-line m emory m odules (SIMM's), which are
organized as either 256K x 9 bits or 1M x 9 bits depending on the version of the Little Board that
you are using. At least two SIMM's are required for operation, and the board must be jumpered
to indicate whether two or four are being used. Note that when only two SIMM modules are
used, they must be inserted in positions U1 and U2, with U3 and U4 left empty.
An additional jumper option, available for systems with 1 megabyte or more of DRAM memory
installed, allows the memory above the normal 640K byte system memory area to be used as
"extended memory" if desired. When the extended memory option is enabled, it begins at address
100000h.
Three jumpers (W3, W4, W5) must be set as shown in Table 2-5, to indicate the number (2 or 4)
and type (256K or 1M) of onboard SIMM DRAM memory that is installed. Note that all four
SIMM DRAM modules must be the same type (i.e. 256K or 1M).