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PCD5003A Datasheet(PDF) 10 Page - NXP Semiconductors |
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PCD5003A Datasheet(HTML) 10 Page - NXP Semiconductors |
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10 / 44 page  1999 Jan 08 10 Philips Semiconductors Product specification Enhanced Pager Decoder for POCSAG PCD5003A If any message code-word is found to be uncorrectable, ‘data-fail’ mode is entered and no data transfer will be attempted at the next sync word position. Instead, a test for sync word will be carried out. In the data fail mode message reception continues normally for 1 batch duration. Upon detection of sync word at the expected position the decoder returns to ‘data receive’ mode. If sync word again fails to appear, batch synchronization is deemed lost. Call reception is then terminated and ‘fade recovery’ mode is entered. The fade recovery mode is intended to scan for sync word and preamble over an extended window (nominal position ±8 bits). This is done for a period of up to 15 batches, allowing recovery of synchronization from long fades in the radio signal. Detection of preamble switches to ‘preamble receive’ mode, while sync word detection switches to ‘data receive’ mode. When neither is found within a period of 15 batches, the radio signal is considered lost and ‘carrier off’ mode is entered. The purpose of carrier off mode is to detect a valid radio transmission and synchronize to it quickly and efficiently. Because transmissions may start at random, the decoder enables the receiver for 1 code-word in every 18 code-words looking for preamble or sync word. By using a buffer containing 32 bits (n bits from the current scan, 32 − n from the previous scan) effectively every batch bit position can be tested within a continuous transmission of at least 18 batches. Detection of preamble switches to ‘preamble receive’ mode, while sync word detection switches to ‘data receive’ mode. 7.13 Call termination Call reception is terminated: • Upon reception of any address code-word (including idle code-word) requiring no more than single bit error correction • Upon reception of a correctable address code-word (error type other than ‘111’; see Table 10) that matches an enabled RIC • When a forced call termination command is received from an external controller. • In ‘data fail’ mode, when a sync word is not found at the expected batch position. The last method permits an external controller to stop call reception depending on the number and type of errors which occurred in a call. After a forced call termination the decoder will enter ‘data fail’ mode. The type of error correction as well as the call termination conditions are indicated by status bits in the message data output. In the event of the terminating code-word matching an enabled RIC, a concatenated call will be started with the call header replacing the terminator of the previous call. Following call termination, transfer of the data received since the previous sync word period is initiated by means of an interrupt to the external controller. 7.14 Enhanced call termination The PCD5003A provides an enhanced mode of call termination which is enabled by setting SPF byte 3, bit D7. When enabled, the following call termination conditions apply, in addition to those listed in Section 7.15. • Reception of two consecutive code-words (excluding sync word), each of which are either uncorrectable or an address code-word with more than one bit in error. 7.15 Call data output format POCSAG call information is stored in the decoder SRAM in blocks of 3 bytes per code-word. Each stored call consists of a call header, followed by message data blocks and concluded by a call terminator. In the event of concatenated messages the call terminator is replaced with the call header of the next message. An alert-only call only has a call header and a call terminator. The formats of a call header, a message data block and a call terminator are shown in Tables 4, 6 and 8. A Call Header contains information on the last sync word received, the RIC which began call reception and the type of error correction performed on the address code-word. A Message Data block contains the data bits from a message code-word plus the type of error correction performed. No deformatting is done on the data bits: numeric data appear as 4-bit groups per digit, alphanumeric data have a 7-bit ASCII representation. The Call Terminator contains information on the last sync word received, information on the way the call was terminated (forced call termination command, loss of sync word in ‘data fail’ mode) and the type of error correction performed on the terminating code-word. |
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