MC145572PB Freescale Semiconductor, MC145572PB Datasheet - Page 161

• Manufacturer Part Number: MC145572PB
• Manufacturer: Freescale Semiconductor

Specifications of MC145572PB

• Number Of Line Interfaces: 1
• Control Interface: HDLC
• Lead Free Status / Rohs Status: Not Compliant

Freescale Semiconductor, Inc.
9.6
D CHANNEL COMMUNICATION VIA THE SERIAL OR PARALLEL
CONTROL PORT
In non–ISDN applications, such as pair–gain multiplexing, it is often necessary to communicate low–
speed status information. The MC145572 provides a simple means to transmit this type of status
information over the D channel of the U–interface.
In pair–gain applications, the off–hook status is transmitted from the Remote Terminal (RT) to the
Central Office Terminal (COT) and the ring detect status is transmitted from the COT to the RT (see
Figure 9–3).
In MCU mode, the MC145572 provides a means to transmit and receive D channel information through
the SCP or PCP. This allows an MCU to access the D channel without using the D channel port or
the IDL interface. Once activation is achieved, transparent data is enabled and BR10(b1) is set, D
channel data is accessible through Overlay register OR12. If IRQ3 is enabled and BR10(b1) = 1, a
special code is loaded into NR1 (NR1 = 1111) to indicate that a new byte of D channel data was
received. This interrupt occurs every 500 s. When an activation interrupt (also IRQ3) occurs at the
same time as a D channel interrupt, it is latched and generates an interrupt to the MCU after D Channel
register OR12 has been read. This must be taken into account when writing the interrupt service
routine.
The following two procedures are a basic example of how to communicate over the D channel using
the PCP/SCP registers. DCH_init is used to enable IRQ3 and initiate activation. The interrupt service
routine, DCH_ISR, then enables customer data when activation is achieved and handles the D chan-
nel communications through Overlay register OR12.
OFF-HOOK STATUS
U-INTERFACE
COS
COT
RT
RING-DETECT STATUS
Figure 9–3. Status Information Flow in a 4:1 Pair–Gain Application
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MC145572
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