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8254A COUNTER 2 DATA - ADC PACER DIVIDER UPPER
BADR3 + 2
READ/WRITE
D0D1D2D3D4D5D6D7
01324567
Counter 1 provides the lower 16 bits of the 32-bit pacer clock divider. Its output is fed to the clock input of Counter 2
which provides the upper 16-bits of the pacer clock divider. The clock input to Counter 1 is a precision 10MHz oscillator
source.
Counter 2 output is called the 'Internal Pacer' and can be selected by software to the be the ADC Pacer source. Counters 1
& 2 should be configured to operate in 8254 Mode 2.
ADC 8254 CONTROL REGISTER
BADR3 + 3
WRITE ONLY
D0D1D2D3D4D5D6D7
01324567
The control register is used to set the operating Modes of 8254 Counters 0,1 & 2. A counter is configured by writing the
correct Mode information to the Control Register followed by count written to the specific Counter Register.
The Counters on the 8254 are 16-bit devices. Since the interface to the 8254 is only 8-bits wide, Count data is written to the
Counter Register as two successive bytes. First the low byte is written, then the high byte. The Control Register is 8-bits
wide. Further information can be obtained on the 8254 data sheet, available from Intel or Harris.
7.5.2 DIGITAL I/O DATA AND CONTROL REGISTERS
he 24 DIO lines on the PCI-DAS1000 are grouped as three byte-wide I/O ports. Port assignment and functionality is identi-
cal to that of the industry standard 8255 Peripheral Interface. Please see the Intel or Harris data sheets for more
information.
DIO PORT A DATA
BADR3 + 4
PORT A may be configured as an 8-bit I/O channel.
READ/WRITE
D0D1D2D3D4D5D6D7
01324567
DIO PORT B DATA
BADR3 + 5
PORT B may be configured as an 8-bit I/O channel. Its functionality is identical to that of
PORT A.
READ/WRITE
D0D1D2D3D4D5D6D7
01324567
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