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C96 Memory backup Cap? F1 PTC fuse F2  PTC fuse LK1 Speaker LK2 Header for ? LK3 LK4 OSC1 3.6864 MHz osc OSC2 25.0000 MHz osc SK1 Modem SK2 ISDN SK3 DB15 ethernet (AUI) SK4 Audio In/Out SK5 Headphone SK6 Serial SK7 ?? SK8 KB/Mouse port SK9 PS/2 Mouse SK10 Video SK11 Appleprint ? SK12 SCSI

SK13 DC Power plug SK14 40 pin VMC SK15 Dual PCMCIA slots SK16,17 72 pin SIMMs SK18 SK19 SW1 Switch for? U1 AT&T T 7213 U2 AT&T T7259 DBRI U3 LT LTC1320CS U4 ROS 1.21 2792 U5 Ramtron FM1608S-250SC U6 NCR NCR89C100 U7 EPROM "W/Wort Modem" U8 VLSI VY27004-2TS103-A Y1 H20.000B3 xtal Y2 H12.2960B4 xtal Y3 H16.9344B4  Y4 35.2512 xtal Y5 H19.6608C4 1

U8 is Tadpole TS103-A

SW1 is an "MW" from England, 19N502EB
Case closed microswitch. 

T7259 Dual Basic Rate ISDN chip

FM1608  64K bit Ferroelectric Nonvolatile RAM  from ramtronics.  This is a ferroelectric technology part that acts just like RAM in the circuit, but keeps its memory when the power is off. It provides data retention for 10 years.

SK14 40 Pin SCSI Connector

  This little bad boy uses a 40 pin mini-centronics connector (like the IBM SCSI connectors). Nothing like this in PS/2 land, that's for sure. The planar socket has a male connector.

Removable Hard Drive SCSI Connector

Signal	Pin	Pin	Signal
MOTORVCC	1	21	MOTORVCC
MOTORGND	2	22	MOTORGND
/SCSIIO	3	23	GND
/SCSICD	4	24	SCSID(7)
/SCSISEL	5	25	GND
/SCSIREQ	6	26	SCSID(6)
/SCSIRST	7	27	GND
/SCSIMSG	8	28	SCSID(5)
/SCSIIACK	9	29	GND
/SCSIATN	10	30	SCSID(4)
GND	11	31	GND
/SCSIBSY	12	32	SCSID(3)
GND	13	33	GND
/SCSITPWR	14	34	SCSID(2)
/SCSID(P)	15	35	GND
NC	16	36	SCSID(1)
NC	17	37	GND
/MOTOROFF	18	38	SCSID(0)
GND	19	39	GND
MOTORVCC	20	40	MOTORVCC

NCR89C100 / NCR89C105
  ..used the Machio/Slavio chipset for SCSI (fast-narrow, 8 bit), Ethernet (10base-T or AUI), serial and parallel ports, controlling the Boot PROM and NVRAM/hostid chip, and a bunch of other stuff.  Part numbers for these chips were STP2000QFP (Machio) STP2001QFP (Slavio), aka NCR89C100 / NCR89C105. Performance is for all intents and purposes identical on all systems using the chipset, as far as I have ever been able to tell. SCA connectors for the SS20 was purely a physical interface issue, and in no way utilized the 16-bit interface on the drives, as the bus and controllers were 8-bit.

Slow I/O Subsystem
   The Slow I/O subsystem is managed by an NCR89C105 SLAVIO. The
SLAVIO is an application specific integrated circuit (ASIC), designed as
part of a two-chip set with the NCR89C100 MACIO, which provides two
serial channels, keyboard and mouse ports, an interrupt controller and two
counter-timers. The key features of the SLAVIO include:
 Two synchronous/asynchronous serial ports (85C30 SCC compatible)
 Keyboard/mouse ports (85C30 SCC sub-set)
 Two programmable counter-timers (500ns period)
 Interrupt controller
 8-bit expansion bus (EBus) interface/controller for EPROM and 8-bit
I/O devices
 Internal 82077 style floppy disk controller
 Miscellaneous I/O functions.

Fast I/O Subsystem
The Fast I/O Subsystem includes the SCSI, parallel and network interfaces.
These are controlled by the NCR89C105 MACIO. This device is a custom
ASIC designed to be operated with the NCR89C100 SLAVIO as a
two-chip set. The key features of the MACIO include:
 53C90 style SCSI controller (Emulex FAS100A compatible)
 7990 style Ethernet controller
 Parallel port interface
 Dual 64 byte FIFOs
 IEEE-1496 SBus DMA controller
This section describes each of these features.

Ethernet Controller
The Ethernet controller provides a 10Mbit/sec networking interface. The
design features an AT&T serial interface encoder to provide the standard
AUI interface through a 26-way high density connector. An AUI cable and
an Ethernet transceiver can be used to provide access to other physical
Ethernet media, including Thick, Thin and Fiber-optic networks.
Note
The AUI interface is DC coupled, and any attachment units used with SPARCbook 3 must feature the network isolation function. Ethernet data transfers are supported with the MThe Ethernet interface on the SPARCbook is provided by an NCR92C990 integrated into the MACIO. This provides AUI connections via a 15-pin D-shell connector. The MACIO enhances Ethernet operations by providing DMA support.ACIO DMA function.
 

ISDN and 16-Bit Audio Controller
The ISDN and Audio interface consists of two major components: the
AT&T T7259 Dual Basic Rate ISDN Controller; and the Crystal
Semiconductor Corporation CS4215 Multimedia Audio CODEC.
The T7259 has the following major features:
 Simultaneous terminal endpoint (TE) and network termination (NT)
 CCITT I.430/ANSI T1.605 support for 4 wire ISDN 2B+D basic
access at the S/T reference point
 Multiframing support: S&Q channel operation
 Automatic synchronization of ISDN interfaces
 On-chip HDLC formatter
 On-chip 16-channel DMA address generator and linked list buffer
manager
 Supports AT&T Concentration Highway Interface (CHI)
 Sbus master and slave interface
The ISDN controller combines a DMAC and data format converter
(Parallel/Serial, Serial/Parallel and Time-Division-Multiplex). It has a
number of DMA channels that can be allocated to support the ISDN or
audio functions. The DMACs provide linked-list command support, and FIFOs allow burst data transfers to be performed on the Sbus. Large
amounts of ISDN or audio information can be moved to and from the Sbus
with a minimum of processor overhead. The data is formatted by the ISDN
controller into a composite digital serial stream (the Concentration
Highway Interface). This connects to additional on-chip ISDN support
circuitry, and to the external audio CODEC. The ISDN interface is
implemented as a 2B+D Terminal Endpoint.
The Concentration Highway Interface of the ISDN circuitry provides a
variety of different serial digital framing standards and data rates to the
Audio CODEC. This supports a majority of the world standard Digital
Audio formats. Typical configurations include high-quality stereo 16-bit
44.1KHz (CD), and telephony quality mono 8-bit 8KHz (ISDN).
The CS4215 Audio CODEC has the following major features:
 Stereo analog-to-digital and digital-to-analog conversion
 4KHz to 48KHz sample rates
 16-bit linear and 8-bit u-law or A-law coding
 Serial digital interface, compatible with AT&T CHI Concentration
Highway Interface
 Microphone and line analog outputs

Baud Rate Clocks
A 19.66 MHz clock (Y5) signal generated by the MACIO is used to derive a baud rate clock for all of the SCCs. This is divided by four before being fed to the SCCs at 4.915 MHz. The baud rate can be changed by loading
different time constants (which can be different for each channel) into the
time constant register. The clocking modes 1, 2, 16, 32 and 64 are
supported.

SCSI Controller
The MACIO incorporates an enhanced NCR53C90 Fast SCSI Controller (FSC), which supports SCSI-2 operations at up to 10 Mbytes/sec running
synchronously. SCSI transfers are supported by the MACIO’s integral DMA controller.

Bottom View

F1 PTC fuse F2 picofuse (rework?) U1-8 MT42C8255DJ-8 U9 PPC601 FD66-1PQ U10 VLSI VY27002-2  U11 Rockwell C2900-20

U12 Bt445KHF U13 Benchmarq bq2001S U14 NCR89C105-B U15 Crystal CS4215-KL U16 Rockwell RC144DPL 1

U10  Tadpole TS102-A PCMCIA Controller
Crystal CS4215-KL spec sheet