3.3 TIMING
This section describes the timing characteristics for Tag reading when the Interface is connected to a
number of Addressable Readers. There is a tradeoff between the speed a Tag can travel past a
Reader’s Antenna, and the number of Readers installed on a single Model 2022 Interface. Also
impacting the speed quotient is the size of the Antenna and the read window it produces.
We can supply you with a document that equates Antenna sizes and the number of Readers installed on
an Interface to the physical Tag speed possible.
There is also a tradeoff between Tag data capacity and Tag processing speed, which of course affects
the speed issues discussed above. To increase physical Tag speeds to an even greater level, there
exists a Model 2022/8, the slash 8 standing for 8 character Tags instead of the normal 16. While not
heavily marketed, since it reads Tags programmed with shorter data strings, the Model 2022/8 can
detect, process, and transmit the messages faster.
Section 3.3.1 below discusses the timing characteristics of the Model 2022 at length. Because the two
models are so similar, the discussion applies also to the Model 2022/8. Only parameter values change.
Section 3.3.2 summarizes the equations and parameters used in the calculations of section 3.3.1, but
also includes the parameters for the Model 2022/8.
3.3.1 WORSE CASE TAG REPORT TIMING
This section deals with what's referred to in computer jargon as "worst case" situation. The worst-case
situation that is addressed here is if 16 Readers are connected to a Model 2022 Interface and a Tag
arrives at each one at the exact same time: how long will it take to report all of them, and what is the
fastest the Tags can be moving past the Reader’s Antenna and still all be detected. Mode 1 operation is
also assumed.
The delay until the 16
th
Tag is reported is dependent on the baud rate used to transmit the Tag data.
Obviously, if the Model 2022 Interface is transmitting at 110 baud it will take much longer to report 16
Tags than at 19,200. Each Tag takes approximately 50 milliseconds, worst case, to detect and
process. Add to this the transmission time: 20 characters per Tag (16 data characters, 2 characters for
channel ID, BOM Line Feed, and EOM Carriage Return) times 12 bits per character (worst case: 1
Start bit, 8 data bits, 1 parity bit, and 2 Stop bits) makes 240 bits transmitted per Tag. At 110 baud
(bits per second) each Tag takes over 2 seconds to transmit, at 19,200 baud each Tag takes only 12.5
milliseconds (.0125 seconds). Adding the 50 millisecond processing time to the transmission time and
multiplying it by 16 Readers gives the following worse case delays for the last Tag when 16 hit the
Reader simultaneously:
BAUD RATE SYSTEM DELAY
110 35.71 seconds
300 13.60 seconds
600 7.20 seconds
1200 4.00 seconds
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