DS2152L datasheet(55/94 Pages) DALLAS

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DS2152

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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)

FDL Interrupt Mask Register (FIMR)

general control over the HDLC and BOC controllers key

status information for both transmit and receive directions

allows/stops status bits to/from causing an interrupt

Receive PRM Register (RPRM)

Receive BOC Register (RBOC)

Receive FDL FIFO Register (RFFR)

status information on receive HDLC controller status

information on receive BOC controller access to 16-byte

HDLC FIFO in receive direction

Transmit PRM Register (TPRM)

Transmit BOC Register (TBOC)

Transmit FDL FIFO Register (TFFR)

status

information

transmit

HDLC

controller

enables/disables transmission of BOC codes access to 16-byte

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

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.

DS2152L Datasheet(PDF) 55 Page - Dallas Semiconductor

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