SECTION 2 - INTRODUCTION
The SGS - Thomson MK50H25 Link Level Controller is a VLSI semiconductor device which provides complete link level data communications control conforming to the 1984 and 1988 CCITT versions of X.25. The MK50H25 will perform frame formating including: frame delimiting with flags, transparency (so-called "bit-stuffing"), error recovery by retransmission, sequence number control, S (supervisory) and U (unnumbered) frame control, plus FCS (CRC) generation and detection. The MK50H25 also supports X.75 and X.32 (with its XID frame support), as well as single channel ISDN LAPD (with its support of UI frames and extended addressing capabilities).

SECTION 1 - FEATURES
■ System clock rate up to 33 MHz (MK50H25 - 33), 25 MHz (MK50H25 - 25), or 16 MHz (MK50H25 - 16).
■ Data rate up to 20 Mbps continuous (MK50H25 - 33) or up to 51 Mbps bursted
■ On chip DMA control with programmable burst length.
■ DMA transfer rate of up to 13.3 Mbytes/sec using optional 5 SYSCLK DMA cycle (150 nS) at 33 MHz SYSCLK.
■ Complete Level 2 implementation compatible with X.25 LAPB, ISDN LAPD, X.32, and X.75 Protocols. Handles all error recovery, sequencing, and S and U frame control.
■ Pin-for-pin and architecturally compatible with MK5025 (X.25/LAPD), MK5027 (CCS#7) and MK5029(SDLC).
■ Buffer Management includes:
    - Initialization Block
    - Separate Receive and Transmit Rings
    - Variable Descriptor Ring and Window Sizes.
■ Separate 64-byte Transmit and Receive FIFO.
■ Programmable Transmit FIFO hold-off watermark.
■ Handles all HDLC frame formatting:
    - Zero bit insertion and deletion
    - FCS (CRC) generation and detection
    - Frame delimiting with flags
■ Programmable Single or Extended Address and Control fields.
■ Five programmable timer/counters: T1, T3, TP, N1, N2
■ Programmable minimum frame spacing on transmission (number of flags between frames).
    - Programmable from 1 to 62 flags between frames
■ Selectable FCS (CRC) of 16 or 32 bits, and passing of entire FCS to buffer.
■ Testing Facilities:
    - Internal Loopback
    - Silent Loopback
    - Optional Internal Data Clock Generation
    - Self Test.
■ Programmable for full or half duplex operation
■ Programmable Watchdog Timers for RCLK and TCLK (to detect absence of data clocks)
■ Option causing received data to effectively be odd-byte aligned, in addition to standard evenbyte alignment.
■ Available in 52 pin PLCC(for use with external ROM), or 48 pin DIP packages.