National CP3BT26 manual IOM-2 Mode, Loopback Mode, 150

CP3BT26

20.6.4IOM-2 Mode

The AAI can operate in a special IOM-2 compatible mode to allow to connect to an external ISDN controller device. In this IOM-2 mode, the AAI can only operate as a slave, i.e. the bit clock and frame sync signal is provided by the ISDN controller. The AAI only supports the B1 and B2 data of the IOM-2 channel 0, but ignores the other two IOM-2 channels. The AAI handles the B1 and B2 data as one 16-bit data word.

The IOM-2 interface has the following properties:

„Bit clock of 1536 kHz (output from the ISDN controller)

„Frame repetition rate of 8 ksps (output from the ISDN controller)

„Double-speed bit clock (one data bit is two bit clocks wide)

„B1 and B2 data use 8-bit log PCM format

„Long frame sync pulse

Figure 73 shows the structure of an IOM-2 Frame.

SFS
STD/SRD	B1 B2 M		C	IC1 IC2 M		C	C
		IOM-2 Channel 0			IOM-2 Channel 1		IOM-2 Channel 2
				IOM-2 Frame (125 µs)

DS162

Figure 73. IOM-2 Frame Structure

Figure 74 shows the connections between an ISDN control- ler and a CP3BT26 using a standard IOM-2 interface for the B1/B2 data communication and the external bus interface (IO Expansion) for controlling the ISDN controller.

	SCK		Bit Clock
	SFS		Frame Sync
CP3BT2x				ISDN Controller
	STD		Data In
	SRD		Data Out
	A[7:0]		Address
	D[7:0]		Data
	SELIO			Chip Select
		RD		Output Enable
					DS241

To connect the AAI to an ISDN controller through an IOM-2 compatible interface, the AAI needs to be configured in this way:

„The AAI must be in IOM-2 Mode (AGCR.IOM2 = 1).

„The AAI operates in synchronous mode (AGCR.ASS = 0).

„The AAI operates as a slave, therefore the bit clock and frame sync source selection must be set to external (ACGR.IEFS = 1, ACGR.IEBC = 1).

„The frame sync length must be set to long frame sync (ACGR.FSS = 1).

„The data word length must be set to 16-bit (AGCR.DWL = 1).

„The AAI must be set to normal mode (AGCR.SCS[1:0] = 0).

„The internal frame rate must be 8 ksps (ACCR = 00BE).

20.6.5Loopback Mode

In loopback mode, the STD and SRD pins are internally connected together, so data shifted out through the ATSR register will be shifted into the ARSR register. This mode may be used for development, but it also allows testing the transmit and receive path without external circuitry, for ex- ample during Built-In-Self-Test (BIST).

Figure 74. CP3BT26/ISDN Controller Connections

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