DS80C320-MCG Datasheet, PDF (153/175 Pages) Dallas Semiconductor – High-Speed Microcontroller User Guide

High-Speed Microcontroller User’s Guide
MULTIPROCESSOR COMMUNICATION
Multiprocessor communication mode makes special use of the 9^th data bit in Modes 2 and 3. In the
original 8051, the 9^th bit was restricted to a 0 or 1 condition, but had no special purpose. In the 80C32
and the High-Speed Microcontroller, it can be used to signify that the incoming byte is an address. This
allows the processor to be interrupted only if the correct address appears. The receive interrupt, if
enabled, will only occur when a recognized address is received.
When a serial word is received with the 9^th bit set and the appropriate smz=1, the byte will be assumed to
be an address. The address will be compared to an internally stored address. If it matches, a receive
interrupt will occur. The internal address is derived from the contents of two registers. The first register
specifies an absolute address. This is the user specified address of the device. The second register tells
the comparator which address bit(s) to actually use in the comparison. This allows broadcast
transmissions that reach groups of microcontrollers or all microcontrollers on a serial port. The user
defines this protocol.
There are two Special Function Registers that support multiprocessor communication for each UART.
These are independent, so that different addresses can be used in each. The registers are SADDR0 or
SADDR1(hex address A9h or AAh) and SADEN0 or SADEN1 (hex address B9h or BAh). The SADDR
register specifies the individual processor’s address. The SADEN identifies address bits that should be
ignored in matching addresses.
Software will write an 8-bit address to the SADDR register. This is the microcontroller’s individual
address. Any bit in SADEN that contains a logic 0 will cause the corresponding bit in SADDR to be
ignored in comparison. Thus logic 0 bits in SADEN create don’t care bit states for address comparisons.
When an address is received, each address bit that is not masked by a don’t care will be compared to the
SADDR. The microcontroller will interrupt on any address that matches this comparison. Any address
that meets this comparison is called a Given Address. The following example shows how one address
can be directed to an individual processor, or two out of three.
Micro 1
SADDR 11110000
SADEN 11111010
–––––––––––––––––––––––––
Given 11110x0x
Micro 2
SADDR 11110001
SADEN 11111001
–––––––––––––––––––––––––
Given 11110xx1
Micro 3
SADDR 11110010
SADEN 11111010
–––––––––––––––––––––––––
Given 11110x1x
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