Calibre UK IC Communication Adapter ICA93LV - Manual (Page 4)

Revision 1.7 Page 3 of 27
09/12/1999
Important Note: Due to the internal operation of the ICA93, it must not be accessed over the PC
bus (read or written) more than once every nine of its own clock cycles. The ICA93 is clocked at
12MHz; therefore it MUST NOT be accessed more than once every 0.75 microseconds. If this
requirement is not observed operation may become erratic. This is usually only encountered in
very fast PCs, however it must be borne in mind when writing software if say the system hardware
might be updated in the future. When timing problems are encountered it is invariably this which
is causing the difficulties, not the selection of the number of wait states. This is automatically
controlled by the Windows DLLs, but must be checked by the programmer when using the DOS
routines.
2.3. Interrupt Generation
The adapter is designed for either polled or interrupt driven operation. Interrupts are generated after the
sending or reception of any byte on the I
2 C Bus. The pulse is negative going with a duration of approx.
100nS, the interrupt being signalled by the rising edge of this pulse.
Link 5 allows the selection of which PC interrupt line the card is connected to:
LK5 position PC Interrupt
NONE DISABLED
2 IRQ2
3 IRQ3
4 IRQ4
7 IRQ7
As can be seen, the card is capable of connecting to four out of the eight available PC I/O interrupts. The
final choice will depend on what other peripherals are connected to the PC.
The standard configuration is with the interrupts disabled, i.e. LK5 in the “NONE” position.
2.4. Bus Termination and Protection
Normally the system to which the I 2 C Communications Adapter is to be connected should already have
master pull up resistors fitted to the SCL and SDA lines. If this is not the case, LK10 and LK12 can be
used to connect 4K7 pull up resistors to the variable supply on these lines. The standard configuration is
with these resistors disconnected.
The SCL and SDA lines are protected by 100R series resistors before exiting the adapter via the 9 way
“D” socket. Upstream of the series resistors, the SCL and SDA pins on the PCF8584 are pulled up with
high value resistors (10K). These ensure that the I
2 C Bus is in a defined state even if no other devices are
connected. The standard configuration is with these resistors connected using LK9 and LK11
LK13 and LK14 connect optional protection diodes to the SCL and SDL lines. When selected, these lines
are clamped to the 0V and variable supply lines giving protection against transients. If these diodes are
connected, the external I
2 C system will not function if the adapter is connected but not powered up. The
standard configuration is with these diodes disconnected.
2.5. Installing the Adapter
NOTE: BEFORE INSTALLING THE ADAPTER IN YOUR PC, OBSERVE ANY SAFETY
PRECAUTIONS GIVEN BY THE MANUFACTURER OF THE COMPUTER.
NORMAL ANTI-STATIC HANDLING PRECAUTIONS SHOULD BE OBSEVED TO
AVOID ANY DAMAGE TO THE ICA93 OR THE COMPUTER.
Switch off the power to the PC and remove the mains plug from its socket before opening the case.
Plug the adapter into any available slot. Ensure the fixing screw is replaced in the computer rear panel to
hold the adapter firmly in place.
Close the case, reconnect the mains lead and switch on the computer.