
BCRTM-21
5.2 Hardware Interface
The BCRTM provides a simple subsystem interface and
facilitates DMA arbitration. The user can configure the
BCRTM to operate in a variety of memory-processor
environments including pseudo-dual-port RAM and
standard DMA configurations.
For complete circuit description, such as arbitration logic
and I/O, please refer to the appropriate application note.
5.3 CPU Interconnection
Pseudo-Dual-Port RAM Configuration
The BCRTM’s Address and Data buses connect directly to
RAM, with buffers isolating the BCRTM’s buses from those
of the host CPU (figures 3a and 3b). The CPU’s memory
control signals (RD, WR, and MEMCSI) pass through the
BCRTM and connect to memory as RRD, RWR, and
MEMCSO.
Standard DMA Configuration
The BCRTM’s and CPU’s data, address, and control signals
are connected to each other as shown in figures 3c and 3d.
The RWR, RRD, and MEMCSO are activated after DMAG
is asserted.
In either case, the BCRTM’s Address and Data buses remain
in a high-impedance state unless the CS and RD
signals are active, indicating a host register access; or
TSCTL is asserted, indicating a memory access by the
BCRTM. CPU attempts to access BCRTM registers are
ignored during BCRTM memory access. Inhibit DMA
transfers by using the Busy function in the Remote Terminal
Address Register while operating in the Remote
Terminal mode.
The designer can use TSCTL to indicate when the BCRTM
is accessing memory or when the CPU can access memory.
AEN is also available (use is optional), giving the CPU
control over the BCRTM’s Address bus. A DMA Burst
(BURST) signal indicates multiple DMA accesses.
Register Access
Registers 0 through 13 are accessed with the decode of the
four LSBs of the Address bus (A0-A3) and asserting CS.
1553 BUS
BUS B
BUS A
XFMR
XFMR
(DUAL REDUNDANT)
BCRTM
CONTROL/ARBITRATION
CONTROL
CPU
HOST
BUFFERS
16 ADDRESS
16 DATA
RAM
DUAL
TRANSCEIVER
TRANSMITTER
TIMEOUT
Figure 3b. CPU/BCRTM Interface -- Pseudo-Dual-Port RAM Configuration