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§ 1703.5. Reader Communications Protocol.

21 CA ADC § 1703.5Barclays Official California Code of Regulations

Barclays California Code of Regulations
Title 21. Public Works
Division 2. Department of Transportation
Chapter 16. Compatibility Specifications for Automatic Vehicle Identification Equipment
Article 4. Reader Specifications
21 CCR § 1703.5
§ 1703.5. Reader Communications Protocol.
Currentness
(a) AM Modulation Scheme.
The downlink (reader-to-transponder) modulation scheme shall be unipolar ASK of the RF carrier using Manchester encoding. A data bit ‘1’ is transmitted by sending an RF pulse during the first half of the bit period and no signal during the second half, while for a ‘0’ data bit the reverse order is used; i.e., no signal during the first half of the bit period and an RF pulse transmission during the second half.
(b) Data Bit Rates.
The data bit rate for reader-to-transponder messages shall be 300 kbps.
(c) Field Strength.
The field strength of a reader data message at the transponder shall be greater than 500 mV/m.
(d) Standard Reader Data Message Format.
The standard portion of a reader data message shall consist of a header and transaction record type code. The subsequent length, data content, and error detection scheme shall then be established by the definition for that transaction record type.
(e) Reader Data Message Formats for AVI.
There may be several reader-to-transponder data message formats. The format is determined by the transaction record type code sent by the reader. The following is the reader-to-transponder message format presently specified for AVI electronic toll collection applications:
(1) Reader Transaction Record Type 1 (Polling Message).
The polling message (which follows the 100 microsecond delay after the trigger signal) tells the transponder the type of transaction the reader wishes to conduct. For AVI electronic toll collection applications, reader transaction record type 1 (polling message) also would identify the agency or toll authority. For AVI applications, the reader-to-transponder type 1 polling message shall be structured using the following ordered data bit fields:
Field Definition
No. Bits
Hexadecimal Value
Header Code
Selsyn
8
AA
Flag
4
C
Transaction Record Type Code
16
8000
Agency Code
16
Error Detection Code
16
Total: 60
(2) Reader Transaction Record Type 2 (Acknowledge Message).
A reader-to-transponder acknowledge data message shall be provided to inform specific transponders that they have been successfully processed and to stop responding to further identical reader polling requests. The acknowledge message is used to terminate the transaction, and is only sent if the transaction is successfully completed. Reader transaction record type 2 (acknowledge message) shall consist of the following ordered data bit fields:
Field Definition
No. Bits
Hexadecimal Value
Header
Selsyn
8
AA
Flag
4
C
Transaction Record Type Code
16
C000
Transponder ID Number
32
Reader ID Number
32
Transaction Status Code
16
Error Detection Code
16
Total: 124
(f) Reader End-of-Message Frame.
The end-of-message signal for reader-to-transponder data messages shall consist of a minimum of 10 microseconds of no RF carrier signal. Transponder decoders shall have the ability to detect this condition as an invalid Manchester code.

Credits

Note: Authority cited: Section 27565, Streets and Highways Code. Reference: Sections 27564 and 27565, Streets and Highways Code.
History
1. Renumbering of former section 1704.5 to new section 1703.5 filed 11-28-2017; operative 1-1-2018 (Register 2017, No. 48).
This database is current through 4/26/24 Register 2024, No. 17.
Cal. Admin. Code tit. 21, § 1703.5, 21 CA ADC § 1703.5
End of Document