Introduction

EnDat is a bidirectional interface for position encoders. During EnDat operation, the EnDat receiver receives position information from the EnDat position encoder.

Note: This implementation using Peripheral input/output mode of PRU-ICSS. Refer Peripheral IF mode for more details.

Features Supported

EnDat 2.2 command set
EnDat 2.1 command set
Interrupted and continuous clock mode
Cable length up to 100m @8MHz
Propagation delay compensation - Automatic estimation of propagation delay
Receive on-the-fly CRC verification of position, parameters and additional information
Two modes of operation - host trigger and periodic trigger
Channel select
Same clock frequency for all channels in multi channel mode within the same PRU-ICSS slice
- Different PRU slices can simultaneously handle encoders operating at different frequencies
Support for periodic trigger using PRU-ICSS IEP timer module
Safety Readiness: Recovery time
Clock up to 16MHz with single channel
Note
In three channel interface of PRU-ICSS, receive (Rx) is oversampled at 8x of send (Tx). Therefore, the encoder interface frequency "f" should be such that Tx source clock value is divisible by "f" and Rx source clock value is divisible by "8*f".
Possible interface speeds with different source clock combinations:

Clock Source
Interface Speed

PRU UART Clock (192 MHz) 1MHz, 2MHz, 4MHz, 6MHz, 8MHz, 12MHz, 16MHz

PRU Core Clock (200 MHz)
1MHz, 5MHz

Features Not Supported

In general, peripherals or features not mentioned as part of "Features Supported" section are not supported in this release, including the below:

Independent clock frequency for each channel in multi channel mode within the same PRU-ICSS slice
- Clock frequency is a PRU-ICSS slice level configuration
- Each channel within the same PRU-ICSS slice in multi-channel mode will have same clock frequencies

Limitations

SysConfig Features

Note: It is strongly recommend to use SysConfig where it is available instead of using direct SW API calls. This will help simplify the SW application and also catch common mistakes early in the development cycle.

Attention: For each PRU-ICSS slice being used for EnDat, one module instance should be created in SysConfig.

SysConfig can be used to configure the following:

Selecting the ICSS instance
Selecting the ICSSM PRU slice (Tested on ICSSM-PRU0)
Configuring PINMUX
Channel selection
IEP event selection for periodic trigger mode
Selecting RX and TX source clock
Booster Pack Support: Enable when using BP-AM2BLDCSERVO

Note: EnDat firmware is tested with ICSS Core Clock running at 200 MHz frequency or ICSS UART Clock running at 192 MHz only.

Periodic Trigger Modes

The EnDat driver supports two types of periodic trigger modes for continuous position sampling:

CMP Mode (Compare Event Mode)

In CMP mode, the IEP timer compare event triggers position sampling. Compare events occur when the IEP timer counter matches the configured compare value. This mode enables fixed-rate periodic sampling.

Configuration:

Compare event range: CMP0-CMP15 (0-15)
Configured via endat_config_periodic_trigger_cmp_mode() API
IEP compare event number set via endat_config_iep_cmp_event() API
Event selection can be done in SysConfig
IEP configuration and CMP event configuration should be done in application. Driver uses above APIs to inform firmware to enable CMP periodic mode and uses the configured CMP event to start sampling periodically.

CAP Mode (Capture Event Mode)

In CAP mode, external signals trigger position sampling through IEP capture events. The capture event is triggered on the rising edge of the external input pulse, enabling event-driven position capture. Internal signals can also be mapped to IEP capture events via XBAR.

Configuration:

Capture event range: CAP0-CAP7 (0-7)
Configured via endat_config_periodic_trigger_cap_mode() API
IEP capture event number set via endat_config_iep_cap_event() API
Event selection can be done in SysConfig
IEP configuration and CAP event configuration should be done in application. Driver uses above APIs to inform firmware to enable CAP periodic mode and uses the configured CAP event to start sampling periodically.

Note

External signal must be routed to IEP capture input (if needed) in application
CAP6 and CAP7 support falling edge detection as well. In EnDat, rising edge is used always.

Attention: Both IEP event configuration APIs (endat_config_iep_cmp_event() and endat_config_iep_cap_event()) are automatically called during endat_init() with values configured in SysConfig.

PRU-ICSS Resource Usage

Utilizes the Peripheral IF mode (3-channel peripheral interface mode) for EnDat communication. Maximum of 3 channels are available per PRU slice. (Refer Peripheral IF mode for more details)
Each channel has 4 pins (Clock, Data out, Data in, Output enable)
Following table contains details of memory usage, IEP usage and interrupt controller usage:

Attention: In addition to the following resources used by PRU firmware, SDK examples also configure IEP0 CMP0 for IEP counter reset in periodic trigger CMP mode.

Configuration per slice

PRU Core(s)

Memory Usage

IEP Usage

Interrupt Controller (INTC) Usage

Description

Single channel

PRUx

DMEM:188 Bytes, from offset 0x00 to 0xBB offset
IMEM: ~ 5.57 kB
TCMB0: 40 Bytes, 40 Bytes of memory can be located anywhere within the offset range 0x00 to 0x78, depending on the selected channel.

CMP Mode: IEP0 CMPy for trigger (CMPy selected in SysConfig)
CAP Mode: IEP0 CAPy for trigger (CAPy selected in SysConfig)

INTC event/input number 18 or 21 (pr0_pru_mst_intr[2/5]_intr_req) is used to trigger interrupt to Arm® Cortex®-R5F based on slice

IEP, CMP/CAP events and INTC signal are used only in periodic trigger modes

Attention: TCMB0 memory is a part of R5F, not PRU-ICSS.

Note: For pin usage, see Pin Multiplexing section.

ENDAT Design

EnDat Protocol Design explains the design in detail.

Example

EnDat Diagnostic

API

APIs for ENDAT Encoder

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