SERIES PMC341 PCI MEZZANINE CARD SIMULTANEOUS ANALOG INPUT MODULE
___________________________________________________________________________________________
- 11 -
Table 3.5: Digital Output Codes and Input Voltages
DESCRIPTION
ANALOG INPUT
Model
PMC341 (14-bit)
Least Significant
Bit Weight
1.22mV
+ Full Scale
Minus One LSB
9.998779
Volts
7FFC
hex
Midscale
0V
0000h
One LSB Below
Midscale
-1.22mV
FFFC
hex
Minus Full Scale
-10V
8000
hex
Reference Voltage Access Register (Write, 1CH)
This register is used to initiate a read of the reference voltage
value. The reference voltage value is provided so that software
can adjust and improve the accuracy of the analog input voltage
over the uncalibrated state. The reference voltage is precisely
measured at the factory and then stored to this location at the
addresses given in table 3.6.
The Reference Voltage Access Register is a write-only
register and is used to configure and initiate a read cycle to the
Reference Voltage memory. Setting bit-15 of this register high, to
a “1’’, initiates a read cycle. Setting bit-15 of this register low, to
a “0’’, initiates a write cycle.
The address of the Reference Voltage to be read must be
specified on bits 14 to 8 of the Reference Voltage Access
register.
Reference Voltage Access Register
Read or
Write~
Address
Write Data
15
14, 13, 12, 11, 10, 9, 8
7 down to 0
The reference voltage is stored in memory as a null
terminated ASCII character string. For example if the value
4.99835 were stored to memory the corresponding ASCII
characters would be 34, 2E, 39, 39, 38, 33, 35, 00 as shown in
Table 3.6. Note, the ASCII equivalent of a decimal point is 2E
and the null character is 00. The memory should be read starting
at address 00 until the null ASCII character is read. This string
can then be converted into a float by using your compiler’s ATOF
function.
Table 3.6: Reference Voltage Address Memory Map
Address (Hex)
00
01
02
03
04
05
06
07
Example Reference Value
4
.
9
9
8
3
5
null
ASCII Characters As Stored In Memory
34
2E
39
39
38
33
35
00
The address corresponding to each of the reference voltage
digits is given in hex. The most significant digit is stored at
address 00 hex.
For additional details on the use of the reference voltage,
refer to the “Data Correction” section.
Write accesses to the Reference Voltage Access register are
possible via 32-bit or 16-bit data transfers, only. Storing the
reference voltage value to memory is normally only performed at
the factory.
A software or hardware reset has no affect on this register.
Reference Voltage Read Data/Status Register (Read, 20H)
The Reference Voltage Read Data/Status register is a read-
only register and is used to access the read data and determine
the status of a read cycle initiated by the Reference Voltage
Access register. In addition, this register is used to determine the
status of a write cycle to the memory. When bit-1 of this register
is set it indicates the memory is busy completing a write cycle.
All read accesses to this Data/Status register initiate an
approximately 1millisecond access to the memory.
Thus, you
must wait 1 millisecond after reading this Data/Status
register before a new read or write cycle to the memory can
be initiated, (an EEPROM latency limitation).
A read request, initiated through the Reference Voltage
Access register, will provide the addressed digit of the reference
voltage on data bits 15 to 8 of the Reference Voltage Data/Status
register. Although the read request via the Reference Voltage
Access register is accomplished in 200 nano seconds, typically,
the reference voltage digit will not be available in the Reference
Voltage Data/Status register for approximately 2.5 milliseconds.
Bit-0 of the Reference Voltage Data/Status register is the
read complete status bit. This bit will be set high to indicate that
the requested reference voltage digit is available on data bits 15
to 8 of the Reference Voltage Data/Status register. This bit is
cleared upon initiation of a new read access of the memory or
upon issue of a hardware reset.
Reference Voltage Read Data/Status Register
Read Data
Not Used
Write
Busy
Read
Complete
15 Down to 8
7 Down to 2
1
0
Writes to Reference Voltage memory require a special
enable code and are normally only performed at the factory. The
module should be returned to Acromag if the reference voltage
must be re-measured and stored to memory.
A write operation to the memory, initiated via the Reference
Voltage Access register, will take approximately 5 milliseconds.
Bit-1 of the Reference Voltage Data/Status register serves as a
write operation busy status indicator. Bit-1 will be set high upon
initiation of a write operation and will remain high until the
requested write operation has completed. New read or write
accesses to the memory, via the Reference Voltage Access
register, should not be initiated unless the write busy status bit-1
is clear (set low to 0). A hardware reset of the IP module will also
clear this bit.
Read accesses to the Reference Voltage Data/Status
register are possible via 32-bit or 16-bit data transfers, only. A
software or hardware reset will clear all bits to zero.
