IBM 1 Series - Transmit Operations

Transmit Operations
Figure 4-5 is a timing diagram for transmit operations. T,,, is the transmit
time from initiation of a transmit operation to posting of the device-end
interrupt. T,, is nine bit times at the selected bit rate. At 9600 bps (bits
per second), T x0) is 0.936 ms; at 110 bps, Ty, is 81.9 ms. T, is the
transmit load time, measured from the posting of the device-end interrupt
to the time at which the interrupt is accepted and another Write command
can be issued to the adapter without loss of rated performance. T, is two
bit times at the selected bit rate. For 9600 bps, T, is 0.208 ms; at 110
bps, it is 18.2 ms. If a new Write command is executed within time T,, the
character
rate is determined by the adapter clocking; that is, a new
transmit operation is not initiated in less than time T, from the posting of
the device-end interrupt. The adapter however, is ‘“‘write-busy”’ upon
successful execution of the Write command. If a new Write command is
delayed beyond time T,, the transmit operation is initiated immediately
upon successful receipt of the Write command.
Note that the teletypewriter attachment always transmits two stop bits.
WR WR (3) IA (3) IA
\
VS
/
/
WR
/ \
Transmit op Transmit op
—______ _ _) b-
Transmit op ,
C (
<—_—_ lyg——>
—+>| TT) ~— —~| Tl, ~+—
Key:
Baud rate Tyo (milliseconds) Tr (milliseconds) (3)
= post device-end interrupt (condition code 3)
9600 0.936 0.208 IA = interrupt accept by processor
4800 1.87 0.416 WR = Write command accepted
2400 3.74 0.832
1200 7.49 1.66
600 14.98 3.33
300 29.96 6.66
200 44.94 10.0
150 59.9 13.3
110 81.9 18.2
100 89.88 20.0
75
119.08 26.6
50 179.76 40.0
Tyg and T, are +0.1%
Figure 4-5. Transmit operation timing diagram
4-16 GA34-0033