Operational Flow Diagrams - Beehive International B102 Service Manual

character. The output of the character generator
is applied to the parallel-to-serial video shift regis
ter.
Video Shift Register is parallel-to-serial loaded
with data by the low-active signal DPC8 and is
clocked by the main oscillator output. The dots
are shifted out, mixed with cursor information
and blanking signals and applied to the monitor
through the CXDNTRAST control as video infor
mation.
Input/Output Operations UART (Receiver) data
can be received by the B100 Series terminals from
one of three sources: from the two I/O interfaces
into the receive side of the UART or from the
keyboard through the transmit side of the UART
to the receive side of the UART.
The UART is driven by a clock generated inter
nally off the main counter chain. No separate
oscillator is required. A rotary switch located on
the back panel switches the clock rate for oper
ation from 75 to 19200 baud The times-16 clock
isthen applied to the transmitter and receiver of
the UART.
The EIA line receiver receives data at RS232C
levels and gates them into the UART when on line.
Through the same gating, data is brought in from
the transmit side of the UART, where it is con
verted to parallel (7 bits) data.
UART (Transmit) keyboard data lines for bits 1
through 7 are applied to the transmit input data
lines along with the seven BUS lines. Also coming
from the keyboard circuit is a load signal which
triggers the UART to initiate the transmission. As
the UART receives the character for transmission,
it performs the appropriate parity generation, pro
vides one or two stop bits, divides the X16 clock
to get the baud rate, and transmits the character.
The character is applied through an EIA RS232C
interface to the computer or modem.
Also coming from the UART is output data at a
TTL level which is applied to the receiver side of
the UART through the previously mentioned logic
The EIA interface includes a Data Terminal Ready
signal which indicates the status of the unit to the
computer and a Request to Send signal which in
dicates that the terminal has data to send to the
computer. The Clear to Send line coming from the
computer is monitored at the EIA RS232C inter
4-8
face levels. It is received by a line receiver which
converts it to TTL levels and applies it to the UART
clock control circuit to control transmission. An
optional X8 clock (TTL levels) is available as part
of the interface. The BREAK key is on the key
board and enables a timer which holds the transmit
data line in a spacing condition for a predetermined
length of time.
Block Send Circuit allows the operator to compose
a message on the terminal screen and then, depress
ing the SEND key, cause the terminal to send the
entire message to the computer at the selected baud
rate. The sequence of operations is described in
Figure 4-8.
The operation is as follows:
1.
2.
3.
4.
5.
6.
7.
Raise Request-to-Send
When Clear to Send, send STX (002) header
Send data
If FORMAT and END OF PROTECTED FIELD,
send HT code (III3)
If not FORMAT and ENDOF LINE, send
CR/LF sequence (0159/0123)
When end of message, sent ETX (OO33)
Time out and drop Request to Send
Auxiliary Send Circuit is identical to the Block
Send except for two points:
1. The message is transmitted out the AUX
port instead of the Main I/O port
2. The delimiters sent at the start of message,
end of unprotected field, end of line, and
ETX are selected from a different portion
of the Block Send ROM
Special Function (F1-F16) sends a code sequence to
the computer from the terminal. The code is insti
gated by pressinggany one of the 16function keys.
1. An STX is transmitted (0223)
2. An Escape code (O333)
3. Code character (see /\SCII Code Chart, Table 3-2)
4. And ends with an ETX (OO33)
4.3 OPERATIONAL FLOW DIAGRAMS
See Figures 4-7 and 4-9. These diagrams give
the user an outline of the B100/B150 terminal
operation. Specific program information is con
tained in Appendix C and a list of programmable
I. C. part numbers and program numbers is con
tained in the Parts Breakdown Manual.