EM77950
BB Controller
8.3.14 System Status Register (SSR)
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
SSR
-
TX_UF BIT_ERROR LOCK
CS
TX EMPTY
LOCKED
CRC ERROR
This register is a read-only register.
This register provides status information to the MCU concerning the communication
line and the data transfer. Bits 1, 2, 3 can trigger the interrupt if enabled in the IER. Bits
0, 5 and 6 are set by H/W and cleared automatically after the MCU reads the register.
Bits 1~4 are set and cleared by H/W.
Bit 0: CRC_ERROR
This flag indicates a CRC Error in the packet. The CRC Block sets this flag at
the end of each received packet according to the CRC calculation result. BB
compares the calculated CRC and the received CRC. When these values
differ, the flag goes high.
The flag is cleared only after the MCU reads the SSR register. If the MCU does
not read the SSR register, this flag remains “1”.
Bit 1: LOCKED
This flag indicates that a packet is being received.
Bit 1 is set to Logic 1 whenever the system identifies a new incoming packet
(triggers LOCK IN interrupt). The bit will reset to Logic 0 when the packet ends
(triggers LOCK OUT interrupt) or when one of the IDs fails (NET or BYTE).
This indicator is important whenever we want to switch to transmit mode
because it can tell us that the line is busy and that in most cases the
transmission will not succeed. The Lock triggers interrupt for every change in
the bit status.
Bit 2: TX_EMPTY
This bit is the Transmitter Empty flag. When this bit is high the system is
available for loading the next packet for transmission and BB is in receive
mode. When the flag is low, BB is in the middle of a packet transmission.
When transmitting few successive packets, the MCU should wait to the end of
a packet before it reloads the TX_FIFO with the next packet.
Bit 3: CS
Carrier Sense detection bit
When this bit is high, the system has identified a structure of packet
transmission in the air according to CSR.
When low, no carrier has been detected. This bit is only valid in receive mode.
The conditions for setting or clearing this flag are determined in the CS register.
When LOCKED is high, then CS is meaningless.
Product Specification (V1.0) 10.09.2007
(This specification is subject to change without further notice)
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ELAN [ ELAN MICROELECTRONICS CORP ]
