IBM 1 Series - Initial Program Load; Teletypewriter Adapter Operational Characteristics

Initial Program Load
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 IPL source. If no jumper is installed, the
teletypewriter adapter cannot perform IPL.
The IPL record length is 256 bytes, commencing at main storage location
0. The IPL data transfer starts when the adapter recognizes the first non-0
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 manually 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
Data is always transmitted by the teletypewriter adapter in an 11-bit
frame: one start bit, eight data bits, and two 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 the second stop bit is present, it appears to be a
one-bit-time separation 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.
4-12 GA34-0033