Chapter 6
ISA Bus Expansion
Kontron User's Guide PC/104-520
14
6.
ISA Bus Expansion
The design of the PC/104-520 follows the standard PC/104 form factor and offers ISA bus signals for the use
of standard PC/104 adapter cards.
6.1
PC/104 Bus (ISA part)
The PC/104 bus consists of two connectors that use 104 pins in total.
XT bus connector (64 pins)
AT bus connector (40 pins, which is optional for 16 bit data bus system)
The pinout of the PC/104 bus connectors corresponds to the pinout of the ISA bus connectors with some
added ground pins. The two PC systems with different form factors are electrically compatible.
The
XT bus connector
, Row A and B.
The corresponding 64-pin stackthrough header (ISA bus = 62pins) has two added ground pins at the end of
the connector (Pin A32 and Pin B32). The pinout between PC/104 bus and XT ISA bus is identical between
A1 - A31 and B1 - B31.
The
AT bus extension connector
, Row C and D.
The corresponding 40-pin stackthrough header (ISA bus = 36 pins) has four added ground pins, two on each
side of the connector. To avoid confusion, the first two pins are defined as Pin C0 and Pin D0. The additional
ground pins at the end of the connector are defined as C19 and D19. The pinout between PC/104 bus and AT
ISA bus is identical between C1 - C18 and D1 - D18.
6.1.1
PC/104 Connectors
T
he PC/104-520 features both – XT bus and AT bus extension – on two, dual-row socket connector with
2.54mm x 2.54mm grid (0.1” x 0.1”).
The PC/104 XT bus is available through the X4B connector. The PC/104 AT bus is available through the X4C
connector.
A detailed description of the signals including electrical characteristics and timings is beyond the scope of
this document. Please refer to the official ISA bus and PC/104 specifications for more details.
6.1.2
PC/104 Configuration
When using add-on boards on the PC/104 bus, make sure that there are no resource conflicts in the system.
Carefully choose hardware interrupts, DMA channels, memory and I/O address ranges to avoid resource
conflicts, which are often the reason for a board or a feature not functioning correctly.
PC/104 adapter cards are mounted in a stack-through manner. Adapter cards are designed with plugs on
their undersides that mate with the PC/104 socket connectors of PC/104-520. PC/104 adapters can support
the socket connector version on their topside and allow additional stacking of adapters.
Whenever possible use the PC/104-520 as top module of the PC/104 stack as the CPU board is normally the
board with the highest heat dissipation.
