2
FAS216/216U/236/236U
53236-580-00 C
QLogic Corporation
NOTE:
Throughout this data sheet, the term FAS2x6
refers to the FAS216, FAS216U, FAS236, and FAS236U
unless otherwise noted.
Product Description
The FAS2x6 chips are part of the QLogic SCSI
processor family with features designed to facilitate
SCSI-2 support (FAS216 and FAS236) and SCSI-3 support
(FAS216U and FAS236U). The FAS216 and FAS236 can
transfer synchronous data at 10 Mbytes/sec. The FAS216U
and FAS236U can transfer data at 20 Mbytes/sec with
SCAM support. The normal 5-Mbytes/sec transfer rate and
the fast 10-Mbytes/sec transfer rate (FAS216U and
FAS236U) are supported on-chip by setting the FASTSCSI
bit (Configuration 3 register bit 4). Asynchronous transfers
up to 7 Mbytes/sec are also supported. The FAS216U and
FAS236U chips are firmware and pin compatible with the
FAS216 and FAS236 chips, respectively. Figure 1 shows
the FAS2x6 block diagram.
The FAS2x6 replaces existing SCSI interface circuitry,
which typically consists of discrete devices, an external
driver, and a low-performance SCSI interface chip. The
FAS2x6 contains a fast DMA interface; a 16-byte FIFO;
and fast asynchronous and synchronous data interfaces to
the SCSI bus, including drivers in single-ended mode.
Differential mode requires external drivers.
The FAS216 and FAS216U support single-ended
mode; the FAS236 and FAS236U support single-ended and
differential modes. Since the FAS2x6 operates in both
initiator and target modes, it can be used in both host and
peripheral applications. The chip performs such functions
as bus arbitration, selection of a target, and reselection of
an initiator. The FAS2x6 also handles message, command,
status, and data transfers between the SCSI bus and its
internal FIFO or between the SCSI bus and buffer memory.
The chip maximizes protocol efficiency by utilizing a FIFO
command pipeline and combination commands to
minimize host intervention.
Differential Driver Protection
(FAS236/236U Only)
The FAS236/236U pins 5 (DIFFSENS) and 7
(EDIFFS) support the SCSI DIFFSENS differential driver
protection function.
The DIFFSENS function is enabled in differential
mode when pins 5 and 7 are pulled up by an external device.
The FAS236/236U is configured for differential mode
operations when pin 87 (DIFFM) is low. If a single-ended
device or terminator is connected while the chip is
configured for differential operations, DIFFSENS becomes
grounded, disabling the differential drivers. The Gross
Error bit (Status register bit 6) is set and a disconnect
interrupt is generated. The Gross Error bit and the
disconnect interrupt are asserted as long as the DIFFSENS
condition exists. The DIFFSENS function has no effect in
single-ended mode.
SCAM Implementation
The FAS216U and FAS236U support levels 1 and 2 of
the SCAM protocol. SCAM protocol requires direct access
and control over the SCSI data bus and several of the SCSI
phase and control signals. The majority of the SCAM
protocol can be implemented in firmware at
microprocessor speeds. The following SCAM features are
supported in the chip hardware:
s
Arbitration without an ID
s
Slow response to selection with an unconfirmed ID
s
Detection of and response to SCAM selection
System Organization
The FAS2x6 controller systems support three main
buses: the 8- or 16-bit data bus (DB), the 8-bit
microprocessor address and data bus (PAD), and the 8-bit
SCSI bus. The DB provides a path for DMA transfers
through the FIFO. The PAD bus provides access to all
internal registers. The FAS2x6 supports parity
pass-through from the SCSI bus through the FIFO to the
DB. This versatile split-bus architecture separates the two
high-traffic information flows, the SCSI bus and DB bus,
to provide maximum efficiency and throughput. Single- or
split-bus configurations with 8- or 16-bit DMA are pin
selectable. Table 1 shows chip operating conditions.
Interfaces
The FAS2x6 acts as an interface between the
microprocessor and the SCSI bus in target or initiator mode.
The other interfaces are described below:
s
Microprocessor Interface. The DB or PAD bus is
the microprocessor interface to the FAS2x6. Both
buses allow the microprocessor 8-bit read and write
access to all chip registers, including the FIFO. The
PAD bus allows microprocessor interface to the chip
registers independent of DMA activity on the DB.
s
DMA Interface. The FAS2x6 logic transfers data
to and from a buffer over the DB configured as 8 or
16 bits. (Each byte on the bus has its own parity.) If
byte control mode (Configuration 2 register bit 5)
is set, an external DMA controller can dictate how
the bytes are placed on the bus.
Packaging
The pin diagrams for the FAS216/216U and
FAS236/236U are shown in figures 2 and 3. Pins that
support the FAS216/216U and FAS236/236U operations
are shown in figures 4 and 5. Dimensions for the
FAS216/216U 84-pin plastic leaderless chip carrier
(PLCC) and the FAS236/236U 100-pin plastic quad flat
pack (PQFP) are shown in figures 6 and 7.
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