DS2152
There are nine registers that the host will use to operate and control the operation of the HDLC and BOC
controllers. A brief description of the registers is shown in Table 11-1.
HDLC/BOC CONTROLLER REGISTER LIST Table 11-1
NAME
FUNCTION
FDL Control Register (FDLC)
FDL Status Register (FDLS)
general control over the HDLC and BOC controllers key
status information for both transmit and receive directions
FDL Interrupt Mask Register (FIMR) allows/stops status bits to/from causing an interrupt
Receive PRM Register (RPRM)
Receive BOC Register (RBOC)
Receive FDL FIFO Register (RFFR)
Transmit PRM Register (TPRM)
Transmit BOC Register (TBOC)
status information on receive HDLC controller status
information on receive BOC controller access to 16-byte
HDLC FIFO in receive direction
status information on transmit HDLC controller
enables/disables transmission of BOC codes access to 16-byte
Transmit FDL FIFO Register (TFFR) HDLC FIFO in transmit direction
11.1.2 Status Register for the FDL
Four of the HDLC/BOC controller registers (FDLS, RPRM, RBOC, and TPRM) provide status
information. When a particular event has occurred (or is occurring), the appropriate bit in one of these
four registers will be set to a 1. Some of the bits in these four FDL status registers are latched and some
are real-time bits that are not latched. Section 11.1.4 contains register descriptions that list which bits are
latched and which are not. With the latched bits, when an event occurs and a bit is set to a 1, 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. The real-time bits report the current instantaneous conditions that are
occurring, and the history of these bits is not latched.
Like the other status registers in the DS2152, the user will always proceed a read of any of the four
registers with a write. The byte written to the register will inform the DS2152 which of the latched bits
the user wishes to read and have cleared (the real-time bits are not affected by writing to the status
register). The user will write a byte to one of these registers, with a 1 in the bit positions he or she wishes
to read and a 0 in the bit positions he or she does not wish to obtain the latest information on. When a 1 is
written to a bit location, the read register will be updated with current value and it will be cleared. When a
0 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 (for polled driven access) or write-read (for interrupt-
driven access) 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 DS2152 with
higher-order software languages.
Like the SR1 and SR2 status registers, the FDLS register has the unique ability to initiate a hardware
interrupt via the INT output pin. Each of the events in the FDLS can be either masked or unmasked from
the interrupt pin via the FDL Interrupt Mask Register (FIMR). Interrupts will force the INT pin low when
the event occurs. The INT pin will be allowed to return high (if no other interrupts are present) when the
user reads the event bit that caused the interrupt to occur.
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