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SYMBOL
POSITION NAME AND DESCRIPTION
–
CCR6.4
–
CCR6.3
TCLKSRC
CCR6.2
RESR
CCR6.1
TESR
CCR6.0
7 STATUS AND INFORMATION REGISTERS
There is a set of seven registers that contain information on the current real time status of a framer in the
DS21354/554, Status Register 1 (SR1), Status Register 2 (SR2), Receive Information Register (RIR),
Synchronizer status Register (SSR) and a set of three registers for the onboard HDLC controller. The
specific details on the four registers pertaining to the HDLC controller are covered in Section 15 but they
operate the same as the other status registers in the device and this operation is described below.
When a particular event has occurred (or is occurring), the appropriate bit in one of these four registers
will be set to a one. All of the bits in SR1, SR2, and RIR1 registers operate in a latched fashion. The
Synchronizer Status Register contents are not latched. This means that if an event or an alarm occurs and
a bit is set to a one in any of the registers, it will remain set until the user reads that bit. The bit will be
cleared when it is read and it will not be set again until the event has occurred again (or in the case of the
RUA1, RRA, RCL, and RLOS alarms, the bit will remain set if the alarm is still present).
The user will always proceed a read of any of the SR1, SR2 and RIR registers with a write. The byte
written to the register will inform the framer which bits the user wishes to read and have cleared. The user
will write a byte to one of these registers, with a one in the bit positions he or she wishes to read and a
zero in the bit positions he or she does not wish to obtain the latest information on. When a one is written
to a bit location, the read register will be updated with the latest information. When a zero is written to a
bit position, the read register will not be updated and the previous value will be held. A write to the status
and information registers will be immediately followed by a read of the same register. The read result
should be logically AND'ed with the mask byte that was just written and this value should be written
back into the same register to insure that bit does indeed clear. This second write step is necessary
because the alarms and events in the status registers occur asynchronously in respect to their access via
the parallel port. This write–read– write scheme allows an external microcontroller or microprocessor to
individually poll certain bits without disturbing the other bits in the register. This operation is key in
controlling the DS21354/554 with higher–order software languages.
The SSR register operates differently than the other three. It is a read only register and it reports the status
of the synchronizer in real time. This register is not latched and it is not necessary to precede a read of
this register with a write.
Not Assigned. Should be set to zero when written.
Not Assigned. Should be set to zero when written.
Transmit Clock Source Select. This function allows the user to
internally select RCLK as the clock source for the transmit side
formatter.
0 = Source of transmit clock determined by CCR2.2 (LOTCMC)
1 = Force transmitter to internally switch to RCLK as source of transmit
clock. Signal at TCLK pin is ignored
Receive Elastic Store Reset. Setting this bit from a zero to a one will
force the receive elastic store to a depth of one frame. Receive data is lost
during the reset. Should be toggled after RSYSCLK has been applied and
is stable. Must be cleared and set again for a subsequent reset.
Transmit Elastic Store Reset. Setting this bit from a zero to a one will
force the transmit elastic store to a depth of one frame. Transmit data is
lost during the reset. Should be toggled after TSYSCLK has been applied
and is stable. Must be cleared and set again for a subsequent reset.
39 of 117
DS21354 & DS21554
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