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Revision B User Manual
for the VME-SIO4: Board Revision: A
General Standards Corporation
8302A Whitesburg Drive Huntsville, AL 3580, Phone: (256) 880-8787
41
CHAPTER 4: HARDWARE CONFIGURATION
4.0
THE ON-BOARD TRANSMIT/RECEIVE CLOCK
The on-board oscillator, U28, is used for generating a transmit receive clock as well as the on-board clock for the
Zilogs. It is factory installed at 20.0 MHz and may be changed to accommodate a wide range of baud rates. The
desired baud rate is determined by the equation:
(Baud rate) (Time Co 1) = Oscillator frequency of U28
Using the factory installed 20.0 megahertz oscillator frequency of U28, the following time constants will give the
following baud rates:
Time
Constants
Baud
Rates
64
307.2K
256
76.8K
512
38.4K
2048
9.6K
Any standard dip oscillator, 8 pin or 14 pin, will fit into the socket of U28, thereby changing the on-board transmit
receive clock.
4.1
IRQ LEVEL SELECT JUMPERS (J6)
These jumpers are used to select or determine the interrupt request level used by this board.
They use a binary encoded method with jumpers for pins 1 and 2 being the LSB of a 3-bit value. If none of the
jumpers are in, this is a level select of the lowest priority (7). If all the jumpers are installed, this is a level select of 0
and invalid level select.
Examples of different level select configurations are as follows:
4.2
BASE ADDRESS JUMPERS (J1, J4, J5)
Base address selection involves 3 sets of jumpers. They are J1, J4, and J5. J4 is used to select A16 or A24 space and
supervisory or non-supervisory accesses. The jumper for pins 1 and 2 is not installed for address space A24 and is
installed for address space A16. Pins 3 and 4 of J4, is installed for non-supervisory; and not installed for
supervisory.
Pin 1
Pin 5
(a) Set for
Level 5
(b) Set for
Level 2
(c) Set for
Level 3