Intel 8XC196K Series User Manual page 200

The slave port offers an alternative for communication between two microcontrollers. Tradition-
ally, design engineers have had three options for achieving this communication — a serial link, a
parallel bus without a dual-port RAM (DPRAM), or a parallel bus with a DPRAM to hold shared
data.
A serial link, the most common method, has several advantages: it uses only two pins from each
device, it needs no hardware protocol, and it allows for error detection before data is stored. How-
ever, it is relatively slow and involves software overhead to differentiate data, addresses, and
commands. A parallel bus increases communication speed, but requires more pins and a rather
involved hardware and software protocol. Using a DPRAM offers software flexibility between
master and slave devices, but the hardware interconnect uses a demultiplexed bus, which requires
even more pins than a simple parallel connection does. The DPRAM is also costly, and error de-
tection can be difficult. The SSIO offers a simple means for implementing a serial link. The mul-
tiplexed address/data bus can be used to implement a parallel link, with or without a DPRAM.
The slave port offers a fourth alternative.
The slave port offers the advantages of the traditional methods, without their drawbacks. It brings
the DPRAM on-chip, inside the microcontroller (Figure 9-1). With this configuration, the exter-
nal processor (master) can simply read from and write to the on-chip memory of the 8XC196Kx
(slave) processor. The slave port requires more pins than a serial link does, but fewer than the
number used for a parallel bus. It requires no hardware protocol, and it can interface with either
a multiplexed or a demultiplexed bus. The master CPU simply writes to or reads from the device
as it would write or read any parallel interface device (such as a memory or an I/O port). Data
error detection can be handled through the software.
The slave port functions are not available on the 8XC196CA and Jx. The slave
port shared memory mode is available only on the 8XC196KS and KT.
NOTE
CHAPTER 9
SLAVE PORT
9-1