
Yellowknife X4 Hardware Reference Manual
Page 15 /22
Motorola Inc.
Unrestricted Distribution Permitted
98 Feb 20
In full operating mode, VCC = 5V, and the supply current is exclusively due to the SRAM
(the APC does not draw power from the battery in this state) so the current demand is less
than 20mA. VBAT will be supplied through the VCC-to-VBAT diode. The battery pro-
tection diode will be reverse biased so no current drain will occur until VCC drops below
4.15V.
Note also that since the SRAM is not operated at VCC, but at VCC-VF, it is necessary to
insure that inputs do not exceed the SRAM’s maximum ratings of VCC-0.3V by using
low-voltage TTL components to isolate the SRAM from the rest of the system. When the
system is battery powered, the inputs are not driven so limits are cannot be exceeded.
Under system power, the voltage to the SRAM is within this range even at high currents
and low temperatures due to the 3.3V TTL drivers. Variations in the system VCC supply
will match variations in the VSRAM so the SRAM is safe from overvoltages.
2.13 I/O Ports
There are numerous I/O ports on the Yellowknife platform. Some are connectors located
on the back panel in accordance with ATX chassis guidelines, others are attached via
cables. The parallel, keyboard , mouse, and two serial connectors are on the back panel of
the ATX chassis, eliminating cabling. These connectors are equivalent with standard PC-
type connectors. Inside the chassis, the motherboard containsconnectors for cables to IDE
and SCSI disk drives, a oppy disk, and an IrDA transciever.
The oppy connector is a standard CHRP connector, which is not the same as that used on
a PC, though it is very similar. In particular, several pins have been redened:
The keyboard and mouse connections are 6-pin mini-DIN connectors for PS/2-type
devices, similar to most modern PCs. The voltage supply for the keyboard and mouse is
protected by a self-resetting fuse instead of the typical self-destructive fuse, as specied
by the PC’97 guidelines.
The two serial ports are driven with the 75LP185. The ‘LP185 is preferred because it has
the ability to withstand 15kV ESD discharges without external circuitry. Equivalent parts
such as the 75C185 are also available, but without the ESD protection. Many other manu-
facturers make suitable parts that may be used, such as the Maxim MAX211. If non-ESD
protected parts are chosen, additional protection will be needed on the serial port signals.
The IrDA connector allows cabling to a standard IrDA modules available from a wide
variety of sources, such as Hewlett-Packard, Novalog, etc.
Table 3: Floppy Connector Changes
Pin
Old
Function
New
Function
Description
1
GND
F_EJECT#
Low strobe ejects the oppy.
3
GND
NC
Key
4
NC
MSEN0
Media sense 0.