Specifications

158004.B00 41
Pull up resistors of 10k ohms have been added to the SD0 - SD15 data bus signals.
The IOCHRDY, /IOCS16, /MEMCS16 and /ZEROWS signals have 330 ohm pull up
resistors. There are 4K7 pull-up resistors on all IRQ signals on the PC/104 bus and
also on the /IOCHCHK pin. The DREQ signals have 4K7 pull-down resistors.
The TP400 is PC/104 compliant. That is, the TP400 conforms to both the electrical
and mechanical specifications laid down by the PC/104 V2.3 document. There are
some minor limitations on TP400 PC/104 bus operation, which are discussed below.
The TP400 has male PC/104 pins only, and so must be positioned at the top of a
PC/104 stack. This is because the provision for cooling the Geode GX1 chip prevents
a board being stacked on top of it.
The TP400 complies with the mechanical aspects of the PC/104 V2.3 specification.
This includes the use of polarizing pins on the J1 and J2 connectors. Some earlier
versions of the PC/104 specification did not use polarizing pins and it was seen that
this could result in possible misalignment and subsequent product failure if power
was applied before the error was discovered. “Key” positions have been assigned to
the J1 and J2 connectors. These can be seen on the J1 and J2 pin assignment
diagrams detailed in Appendix E. The key positions have had their pin removed and
the socket hole has been blocked to prevent entry by any adjacent pin.
Users should note that any boards produced to PC/104 specifications prior to V2.2
might not mate with V2.2 or V2.3 boards. Prior to the V2.2 specification the key
positions were not present, and J2 could optionally have been a right-angled
connector. The V2.2 and V2.3 specifications do not allow the right-angled J2
connector. Both the J1 and J2 connectors on the TP400 are mounted vertically.
The PC/104 specification (version 2.3) is available on DSP Design's web site
(www.dspdesign.com).
4.3 PC/104-Plus BUS
The PC/104-Plus specification extended the earlier PC/104 specification by adding a
PCI bus interface. This is electrically the same as the PCI bus used in desk-top PCs,
but it uses a high-density 120-pin connector along the opposite edge of the PCB to
the PC/104 (ISA bus) connectors.
The PC/104-Plus bus standard allows existing PC/104 expansion boards to be used,
but also allows for high-performance expansion boards using PCI bus logic chips. An
example of this is the TCVIDEO board from DSP Design, a real-time video capture
board that digitises PAL or NTSC video and bursts the data across the PCI bus in
real-time into the memory of the Geode processor.
The PC/104-Plus specification allows for the addition of up to four expansion boards
using the PCI bus. PC/104 boards can be included in the system as well. The boards
can be configured by a switch or similar to occupy one of four "slots", slot 1 to slot 4.
(Note that in early BIOSes Slot 1 is not supported, so boards must be configured as
slot2, slot 3 or slot 4.) The on-board Ethernet chip is normally configured as the slot 4
device.
The Geode GX1 processor used on the TP400 has 3.3V PCI bus signals which are