SLLA640 April   2025 ISO1228

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1ISO1228 - Relevant Device Information
  5. 2Parallel and Serial Output Modes
  6. 3Switching Communication Modes During Operation
    1. 3.1 Parallel to Serial
    2. 3.2 Serial to Parallel
  7. 4SPI Functional Modes
    1. 4.1 Normal Mode
      1. 4.1.1 Normal Mode - Read IN8-IN1 Continuously
    2. 4.2 Burst Mode
  8. 5Maximum Data Throughput in Serial Mode
  9. 6Digital Low Pass Filtering of Outputs
  10. 7Summary
  11. 8References

2 Parallel and Serial Output Modes

ISO1228 can be configured in either serial or parallel mode to communicate with an MCU or controller. The COMM_SEL pin (pin 38) selects either serial or parallel mode as shown in the Table 2-1:

Parallel communication mode provides the fastest throughput since each input channel is directly available at the corresponding logic output (pins 35 to 28). However, the serial communication mode enables additional control features of ISO1228, such as reading device inputs, setting digital filters for individual inputs and identifying and clearing system faults (field power loss, wire-break detection, CRC errors, and so on). The MCU can access the digital control registers through SPI read and write commands.

Table 2-1 COMM_SEL (Pin 38) - Communication Mode Selection Table
COMM_SEL = Logic High ISO1228 in serial communication mode using SPI
COMM_SEL = Logic Low ISO1228 in parallel communication mode

Some applications can choose to switch between operational modes to take advantage of the higher throughput of parallel mode and the fault detection and control features of serial mode for a more robust system. A system example can use the following sequence:

  1. Start in serial mode (COMM_SEL = 1) to configure input registers on power-up
  2. Configure individual filters for each channel by writing to register addresses 03h to 06h
  3. Change to parallel mode for higher throughput and less prop delay on OUTx (COMM_SEL=0)
  4. Monitor the nFAULT pin’s state for any fault condition (nFAULT = 0 when a fault occurs)
  5. Change to serial mode if a fault is detected (COMM_SEL=1)
  6. Read fault register (02h) and wire break register (01h) to identify the fault condition. Reading the fault register can clear the nFAULT flag if the cause of the fault is no longer present
  7. Return to parallel mode once faults are cleared (COMM_SEL = 0)

The following sections explains the proper timing needed to switch between modes and make glitch-free transitions.