[Yamaha]

❑ Abstract
YTD439 is a LSI that integrates in a single chip all the communication functions that are necessary for constructing an ISDN terminal with a built-in DSU. The functions of both the DSU (U reference point) and terminal (S/T reference point) are packed into the 100-pin SQFP chip allowing miniaturization of the terminal equipment.
YTD439 has a built-in TD switch function that is necessary for controlling the connection of the B-channel data. By connecting an external CPU, memory, and CODEC, a terminal with a built-in DSU can be configured. In addition, YTD439 has a function that reduces the power consumption by stopping the functions of unused blocks. This is effective for battery-driven terminals.

❍ Features
DSU block
• Conforms to TTC Standards JT-I430 and JT-G961.
• LT (line termination) function and CT (circuit termination) function.
• DSU can be disconnected.

S/T reference point driver/receiver block
• Transition to the sleep state possible by setting an I/O register.

CPU interface block
• 8-bit or 16-bit data bus selectable.
• I/O access through registers.

Layer 1 control block
• Frame assembling and disassembling function.
• I430 TTL output pin

Layer 2 control block
• Built-in LAPD protocol (supports four links).
• Call control and D-channel packet function.

Layer 3 interface block
• Message exchange through I/O access (large 1088-byte FIFO).

B channel HDLC controller
• Supports CRC-CCITT and CRC-32.
• 128k/64k/56k rate adaption

B channel transparent
• Supports PIAFS 64k/32k.
• Flexible rate adaption function.

B channel DATA FIFO
• Transmission and reception: 128-byte FIFO × 2 channels.

TD switch
• Switch circuit for 8 channels of B channel data.
• 512 k to 2,048 kHz PCM highway.

Others
• Terminal block can be disconnected. Power can be cut off.
• Terminal block sleep mode.
• Power supply to the analog block: +5 V.
   Power supply to the digital block: +5 V or 3.3 V.
• 5 V tolerant I/O pin
• 100-pin SQFP.

❍ Applications
• Terminal adapter
• Remote router
• ISDN telephone
• ISDN home telephone
• ISDN Facsimile