BUS CONTROLLER MODE
For data transfers generally, 750ns enable signals
(BUFENN,R/WN etc.) are produced by the terminal with a
250ns strobe signal upon which the data will be valid.
The bus controller terminal provides signals to fetch the
message and write out a report and any associated data. The
HALTREQN and HALTEDN handshake lines operate in a
similar fasion to the BUSYREQN / BUSYACKN RT lines in that
if HALTREQN is taken low the terminal will complete the
current instruction and then halt, taking HALTEDN low to
indicate that it has done so
A BC subsystem may be operated in either a single shot or
table driven mode. In either case, the two least significant
address lines (C0,C1) to the instruction and report word stores
are provided by the terminal. On taking HALTREQN high (for a
minimum of 1us) the subsystem initiates an instruction fetch
cycle which consists of the terminal reading the instruction
word, receive command word and transmit command word
from the instruction store and transferring the data pointer
word from the instruction store to an external data address
latch. Further operation is dependent on the instruction word.
On executing a message sequence the terminal will write
out the report word and either:
1. Increment the instruction address and proceed to the
2. Increment the instruction address and halt,
3. Do not increment the instruction address, interrupt
subsystem and halt.
Any data associated with the command will be transferred
to or from the data store in a similar manner as used by the RT.
Figure 7: Bus Controller Subsystem Interface Signal Transfer