IBM 1 Series - Receive Operations

Receive Operations
Figure 4-6 depicts timing for receive operations. Timings are depicted at
device-rated operation. T,, is the time of a receive operation from
initiation by the device to the posting of an interrupt. It is nine bit times at
the selected frequency. At 9600 bps, T,, = 0.936 ms; at 110 bps, T,, =
81.9 ms.
On receive operations, an attention interrupt is posted at the leading edge
of the first stop-bit time for that character. The interrupt accept and read
(IA & R) must be done before the leading edge of the first stop bit time of
the next character to prevent overrun. T, is equal to the maximum
permissible time the processor can delay in performing an interrupt accept
and read after an attention interrupt is posted. T, is equal to the number
of stop bits sent, plus one (start bit), plus the number of data bits sent, all
multiplied by one bit time. Note that by programming the device for two
stop bits, T, (the amount of time the program has to handle the attention
interrupt) may be increased by approximately 10 percent.
Assuming one stop bit and eight data bits, at 9600 bps, T, = 1.01 ms; at
110 bps, T, = 90.8 ms. Figure 4-6 is a state and timing diagram of
possible receive sequences.
Teletypewriter Adapter Feature 4-17