Initial Proqraid Load; Teletypewriter Adapter Operational Characteristics - IBM Series 1 User Manual

The teletypewriter adapter provides initial program load
(IPL) capability. A field installable jumper on the card
designates the teletypewriter adapter as the primary or
alternate 1PL source. If neither pin is jumpered, the
teletypewriter adapter can not perform IPL.
The IPL record length is 256 bytes, commencing at main
storage location z€ro. The IPL data transfer starts when
the adapter recognizes the first non-zero character from the
attached OEM device.
The OEM device attached to the teletypewriter adapter
must have some means of manually initiating a transmit
operation to the teletypewriter adapter if the OEM device is
to be used for IPL.
This implies that the OEM device must be capable of
~~.!1.I
initiating a read operation from some media (such
as cards, tape, or disk) and transmitting the data to the
teletypewriter adapter.
TELETYPEWRITER ADAPTER OPERATIONAL CHARACTERISTICS
As previously described, data is always
transmi~ted
by the
teletypewriter adapter in an eleven bit frame: start bit, 8
data bits, and 2 stop bits. At the beginning of the first
stop bit, the teletypewriter adapter sends an interrupt
request to the processor to signal the completion of the
current character transmission. This interrupt must be
serviced and another transmit operation initiated by the end
of the second stop bit time if maximum transmission rate is
to be maintained.
Devices that are designed to receive either one or two
stop bits may be attached to the teletypewriter card. If
the device is designed for only one stop bit, the second
stop bit appears to be a one-bit-time separation between
character frames.
The teletypewriter adapter can receive data formatted
with either one or two stop bits. If present, the second
stop bit appears to be a one-bit-time separator between
character frames.
If a device is programmable for either one or two stop
bits, it should be programmed for one stop bit. This
increases the receive data rate of the teletypewriter
adapter by approximately 9 percent.
If a device is programmable for several different data
rates that are supported by the teletypewriter adapter, the
device should be programmed for the highest data transfer
rate that results in reliable operation in the environment
in which the system is placed.
Although the following information describes the
internal operation of the teletypewriter
adapter, it is
presented here as necessary information to understand the
subsequent transmit and receive timing charts.
4-10 GA34-003]