Accessory 24E2
Connecting Limits/Flags to the ACC-24E2
The following diagram illustrates the sinking and sourcing connections to an ACC-24E2. this example
uses 12-24V flags.
Sinking,
Separate
Supply
Sourcing,
Separate
Supply
Loss of Encoder Circuit
The encoder-loss detection circuitry works for differential incremental encoders only. In proper
operation, the digital states of the complementary inputs for a channel (e.g. A and A/) should always be
opposite: when one is high, the other is low. If for some reason, such as a cable connection coming
undone, one or more of the signal lines is no longer driven, pull-up resistors on the input line pull and
hold the signal high.
The encoder-loss detection circuitry uses exclusive-or (XOR) gates on each complementary pair to detect
whether the signals are in the same or opposite states. These results are combined to produce a single
encoder-loss status bit that the processor can read.
This technique requires that both signal lines of the pair have pull-up resistors. Note that this is not the
default configuration of a PMAC as it is shipped. The complementary lines (A/ and B/) are pulled to
2.5V in a voltage-divider configuration as shipped to be able to accept both single-ended and normal
differential inputs. This must be changed to a pull-up configuration which involves reversing a socketed
resistor pack on the ACC-24E2A.
ACC-24E2 Encoder Loss Detection with UMAC Turbo CPU
Channel Resistor
Pack
Status Bit Address
(Even-Numbered
Servo IC)*
Status Bit Address
(Odd-Numbered
Servo IC)*
Status Bit
Name
Bit Error
State
1 RP22 Y:$07xF08,5 Y:$07xF0C,5 QL_1- 0
2 RP24 Y:$07xF09,5 Y:$07xF0D,5 QL_2- 0
3 RP22** Y:$07xF0A,5
Y:$07xF0E,5 QL_3-
0
4 RP24** Y:$07xF0B,5
Y:$07xF0F,5 QL_4-
0
*The x digit in this hex address matches the value (8, 9, A, or B) in the fourth digit from the right in the
board’s own base address (e.g. $079200). If alternate addressing of Servo ICs is used (e.g. Servo IC 2*),
add $20 to these addresses.
**These resistor packs are on the Option 1A piggyback board (if present) of the module, not on the
baseboard.
8
Hardware Setup