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Sabre 1555 RFID & Bar Code Reader Programmer’s Reference Manual
4-12
The reader has received the command, performed the action, and sent a low-level
ACK character, but the ACK character is lost.
Host <=
X
= ACK (ACK character lost)
0x06
The host does not receive the low-level ACK and resends the same frame after the
time-out.
Reader <== <STX> <SMC> <Power_beeps_off> <FM> <CHK> <ETX>
0x7F 0x0D 0x45, 0x5A 0x00 0x01,0xB7 0x7F
The reader has already received this frame (Frame number = 0 in FM byte). The
reader sends a low-level ACK and does not repeat its action.
Host <== ACK (ACK character received)
Implementation Rules
•
The first message sent (or when you want to resynchronize after a restart) must
begin with the <RestartFlag> set to “1” and the <FrameNumber> set to “0”.
•
The <FrameNumber> must be incremented each time a
different frame
is
transmitted.
•
If no low-level acknowledge is received from the product before the low-level
timeout expires, the host can resend the same frame up to two more times with the
same frame number
.
•
To reduce collisions to a minimum, it is necessary to check before transmission if
a frame is being received. In this case, wait until the complete frame is received,
acknowledged, and processed before starting the new transmission.
•
If the low-level response is NAK, this indicates that the corresponding frame was
incorrect:
1.
Bad checksum. This occurs when a character in the frame is lost or if the
proprietary DLE mechanism is not integrated in the checksum itself.
2.
Incorrect frame number. If this is the case, you must resend the same frame
with the “Restart flag” to 1 to resynchronize the product with the host.
•
Host-to-product acknowledgment timeouts:
The low-level and high-level acknowledgments must be sent before their
respective timeouts expire in the product (default timeouts are 100 mS and 500
mS).
Содержание Sabre 1555
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Страница 15: ...1 Before You Begin ...
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Страница 21: ...2 Getting Started ...
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Страница 125: ...A Acronyms and Glossary ...
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Страница 135: ...B Command Value to Base 32 Conversion Table b6 1 ...
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Страница 169: ...E System Specifications ...
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