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SEMI E4-0699 © SE MI 1980, 1999 3 2.1.27 pr imary/secondary att ribute — t h e least signifi- cant bit of the lower message ID which indicate s whether a block belon gs to a pri m ar y or secondary message. 2.1.28 R-bit …
SEMI E4-0699 © SEMI 1980, 1999 2
ISO 2110-1980 — Data Communications, Interface
Connectors and Pin Assignment
1.4.5 SEMI Specifications
SEMI E5 — SEMI Equipment Communications
Standard 2 — Message Content (SECS-II)
SEMI E6 — SEMI Facilities Interface Specification
Format
1.5 Overview of SECS-I — The SECS-I standard
defines point-to-point communication of data utilizing a
subset of the international standard known in the U.S.A.
as EIA RS-232-C and in Japan as JIS C 6361 for the
connector and voltage levels. The actual transmission
consists of 8-bit bytes sent serially with one start and
one stop bit. The communication is bidirectional and
asynchronous, but flows in one direction at a time. The
direction is established by special characters and a
handshake, after which the data itself is sent. Data is
sent in blocks of 254 bytes or less. Each block consists
of a 10-byte header followed by data. A message is a
complete unit of communication in one direction and
consists of 1 to 32,767 blocks. Each block header
contains information for identifying the block as part of
a specific message. Messages are paired by a request
and its reply which together are called a transaction.
1.6 Structure of Document — This document is
divided into sections which correspond to major aspects
of the standard. The sections outline requirements as
well as implications of the requirements. The standard
may be implemented in a variety of ways, depending
upon the computer environment where it is placed.
Implementation is not part of the standard. Information
which may be useful for implementation is included in
the form of Related Information.
2 Terminology
2.1 The following brief definitions refer to sections
providing further information.
2.1.1 ACK — "Correct Reception" handshake code.
(See Section 5.2.)
2.1.2 application software — the software performing
the specific task of the equipment or the host.
2.1.3 block — header plus up to 244 bytes of data.
(See Sections 1.5, 6.7.)
2.1.4 block length — the number of bytes sent in the
block transfer protocol. (See Section 5.6.)
2.1.5 block number — a 15-bit field in the header for
numbering blocks in a message. (See Sections 6.7.)
2.1.6 character — a byte sent on the SECS-I serial
line. (See Section 4.1.)
2.1.7 checksum — a 16-bit number used to detect
transmission errors. (See Section 5.7.)
2.1.8 communication failure — a failure in the
communication link resulting from a failed send. (See
Section 5.4.)
2.1.9 device ID — a 15-bit field in the header used to
identify the equipment. (See Section 6.3.)
2.1.10 E-bit — a bit in the header identifying the last
block of a message. (See Section 6.6.)
2.1.11 ENQ — "Request to Send" handshake code.
(See Section 5.2.)
2.1.12 EOT — "Ready to Receive" handshake code.
(See Section 5.2.)
2.1.13 equipment — the intelligent system which
communicates with a host.
2.1.14 expected block — the block of a message which
is expected by the message protocol. (See Section
7.4.4.)
2.1.15 header — a 10-byte data element used by the
message and transaction protocols. (See Section 6.)
2.1.16 host — the intelligent system which
communicates with the equipment.
2.1.17 length byte — the character used to establish
the block length during transmission. (See Section 5.6.)
2.1.18 line control — a portion of the block transfer
protocol. (See Section 5.8.2.)
2.1.19 master — the block transfer designation for the
equipment. (See Section 5.5.)
2.1.20 message — a complete unit of communication.
(See Section 7.)
2.1.21 message ID — a 15-bit field in the header used
in the process of message identification. (See Sections
6.5, 7.3.1.)
2.1.22 multi-block message — a message sent in more
than one block. (See Sections 6.7, 7.2.2.)
2.1.23 NAK — "lncorrect Reception" handshake code.
(See Section 5.2.)
2.1.24 open message — a multi-block message for
which not all of the blocks have been received. (See
Section 7.4.4.)
2.1.25 open transaction — a transaction in progress.
(See Section 7.3.)
2.1.26 primary message — a message with an odd
numbered message ID. Also the first message of a
transaction. (See Section 6.5.)
SEMI E4-0699 © SEMI 1980, 19993
2.1.27 primary/secondary attribute — the least signifi-
cant bit of the lower message ID which indicates
whether a block belongs to a primary or secondary
message.
2.1.28 R-bit — a bit in the header signifying the
direction of the message. (See Section 6.2.)
2.1.29 receiver — the end of the SECS-I link
receiving a message. (See Section 5.8.4.)
2.1.30 reply — the particular secondary message
corresponding to a primary message. (See Section 7.3.)
2.1.31 reply linking — the process of forming a
transaction out of a primary and a secondary message.
(See Section 7.3.1.)
2.1.32 retry count — the number of unsuccessful
attempts to send a block in the block transfer protocol.
(See Section 5.4.)
2.1.33 RTY — the retry limit or the number of times
the block transfer protocol will attempt to retry sending
a block before declaring a failed send. (See Section
5.4.)
2.1.34 secondary message — a message with an even
numbered message ID. Also the second message of a
transaction. (See Section 6.5.2.)
2.1.35 sender — the end of the SECS-I link sending
message. (See Section 5.8.3.)
2.1.36 slave — the block transfer designation for the
host (See Section 5.5.)
2.1.37 system bytes — a 4-byte field in the header
used for message identification. (See Section 6.8.)
2.1.38 T1 — receive inter-character timeout in the
block transfer protocol. (See Section 5.3.1.)
2.1.39 T2 — protocol timeout in the block transfer
protocol. (See Section 5.3.2.)
2.1.40 T3 — reply timeout in the message protocol.
(See Sections 5, 7.3.2)
2.1.41 T4 — inter-block timeout in the message
protocol. (See Section 7.4.3.)
2.1.42 transaction — a primary message and its
associated secondary message, if any. (See Section 7.3.)
2.1.43 W-bit — a bit in the header signifying that a
reply is expected. (See Section 6.4.)
3 Coupling
3.1 Coupling refers to the physical interface at the
equipment. The host will provide compatible signals at
this point. No restrictions are implied for any interface
other than for equipment covered by this standard.
3.2 Electrical Interface — The connection will include
a serial interface according to EIA Standard RS-232-C
for interface Type E, full duplex communication,
modified by the deletions, additions and exceptions
described in this section.
3.2.1 Connector — Either the 9-pin or 25-pin
connector described in the EIA RS232 may be used. In
the case of the 25-pin connector a female connector will
be mounted on the equipment and a male connector will
be mounted on the cable from the host. In the case of
the 9-pin connector the male connector will be mounted
on the equipment and a female connector will be
mounted on the cable. The connector on the equipment
will have female 4-40 threaded jack screw locks.
NOTE: Suitable 25-pin connectors known as Type "D" are
similar to Amphenol MIN RAC 17 series with jack screw
locks. Suitable 9-pin connector is also Type "D" with
jackscrew locks. It is the type commonly implemented on
desktop and notebook PCs.
3.2.2 Signal Pins — Pins on the connector have
functions as defined in Table 1. Pins 1, 2, 3, and 7 of
the 25-pin connector or pins 3, 2, and 5 of the 9-pin
connector are required for all equipment complying
with SECS-I. When using a 25-pin connector, the two
power supply pins, 18 and 25, are optional as indicated.
Any other pins, if used, shall comply with the RS-232-
C standard.
Table 1 Signal Connections
25-
Pin
9-Pin RS-232-C
Circuit
Circuit Description
1-- AA Shield
2 3 BA Data from Equipment
3 2 BB Data to Equipment
7 5 AB Signal Ground
18 -- -- +12 to +15 volts (opt for
the 25-pin connector)
25 -- -- -12 to -15 volts (opt for
the 25-pin connector)
3.2.3 Logic Levels — For the signal pins 2 and 3, the
logic 1 level will be a voltage less than -3 volts and the
logic 0 level will be a voltage greater than +3 volts.
Voltages will never exceed ± 25 volts. These values
correspond to those specified by the RS-232-C
standard.
3.2.4 Power Supplies — When using a 25-pin
connector, pins 18 and 25 are optional power supplies
for driving external isolation circuits. When provided,
both shall be present and must be able to supply at least
50 mA. (See Related Information R1-2 for example
use.)
SEMI E4-0699 © SEMI 1980, 1999 4
3.3 Data Rate — The supported data rates on signal
pins shall be 9600, 4800, 2400, 1200, and 300 baud.
The same data rate shall apply for data sent to and from
the equipment. The data rate shall be controlled to
better than 0.5%. (See RS-269-B and RS-334.) Optional
rates of 19,200 and 150 baud may be supplied if
desired.
3.4 Physical Medium — The connection with the host
may involve any medium that provides the required RS-
232-C quality, signal levels and data rate at the equip-
ment connector. The quality of signal should be such
that the effective bit error rate is less than 1 × 10
-6
. This
rate can be achieved easily with hardwired systems.
The distance limits specified in RS-232-C apply only to
systems using the wiring technique described in RS-
232-C. Since any method may be used in SECS-I as
long as RS-232-C signals are supplied at the connector,
the distance and isolation is dependent upon the design
of the physical medium which is external to the SECS-I
standard. (See Related Information R1-2.)
4 Character Structure
4.1 Characters — Data will be transmitted or received
in a serial bit stream of 10 bits per character at one of
the specified data rates. The standard character has one
start bit (0), 8 data bits and one stop bit (1). All bit
transmissions are of the same duration. The 8 data bits
are numbered from 1 to 8 in the order sent (see Figure
1). The timing between characters is asynchronous with
respect to the data rate. The 8 data bits may be any
arbitrary code. The eight data bits will hereafter be
referred to as a byte.
Figure 1
Character Structure
4.2 Weighted Codes — For bytes having weighted
codes, bit one is the least significant and bit eight is the
most significant. The most common weighted code is
binary.
4.3 Non-Weighted Codes — For codes without
numeric value such as ASCII, the bit numbers will be
used as the entry into a standard code table for
interpretation of the code. SECS-I performs no parity or
other verification of the contents of individual bytes.
5 Block Transfer Protocol
5.1 The procedure used by the serial line to establish
the direction of communication and provide the
environment for passing message blocks is called the
block transfer protocol. Most of the protocol is
accomplished with a handshake of single bytes. When
both ends of the line try to send at the same time, a
condition known as line contention exists. The protocol
resolves contention by forcing one end of the line,
designated as the slave (always the host), to postpone
its transmission and enter the receive mode.
Retransmission of blocks is used to correct
communication errors. The block transfer protocol is
shown in flow chart form in Figure 2, and described
below. Additional information is also contained in
Related Information R1-3 and R1-4.
5.2 Handshake Bytes — The four standard handshake
codes used in the block transfer protocol are shown in
Table 2. The three letter names, ENQ, EOT, ACK, and
NAK correspond to the ASCII code having the same
pattern.
Table 2 Handshake Codes
Name Codeb8
b7.........b1
Function
ENQ 00000101 Request to Send
EOT 00000100 Ready to Receive
ACK 00000110 Correct Reception
NAK 00010101 Incorrect Reception
5.3 Timeout Parameters — Timeouts are used to de-
tect communications failures. A timeout occurs when
the measured time between two events exceeds a pre-
determined limit. Generally, the length of time that
must pass before it can be assumed that an error has oc-
curred depends upon the particular systems involved.
The time required in one situation might be excessively
long in another. Thus, the timeout values must be
"tuned" to meet the application. In the block transfer
protocol, there are two situations requiring timeout val-
ues. The two timeout values are called parameters T1
and T2.
5.3.1 Inter-Character Timeout, T1 — The inter-
character timeout, T1, limits the time between receipt of
characters within a block after the length byte has been
received and until the receipt of the second checksum
byte.
5.3.2 Protocol Timeout, T2 — The protocol timeout,
T2, limits the time between sending ENQ and receiving
EOT, sending EOT and receiving the length byte, and
sending the second checksum byte and receiving any
character.