Zilog Z16C35 User Manual

Page 259

Application Note

Using SCC with Z8000 in SDLC Protocol

12-4

SYSTEM INTERFACE

(Continued)

Two Z8000 Development Modules containing SCCs are
connected as shown in Figure 4 and Figure 5. The
Transmit Data pin of one is connected to the Receive Data
pin of the other and vice versa. The Z8002 is used as a
host CPU for loading the modules; memories with software
routines.

The Z8002 CPU can address either of the two bytes
contained in 16-bit words. The CPU uses an even address
(16 bits) to access the most significant byte of a word and
an odd address for the least significant byte of a word.

When the Z8002 CPU uses the lower half of the
Address/Data bus (AD7-AD0 the least significant byte) for
byte read and write transactions during I/O operations,
these transactions are performed between the CPU and
I/O ports located at odd I/O addresses. Since the SCC is
attached to the CPU on the lower half of the A/D bus, its
registers must appear to the CPU at odd I/O addresses. To
achieve this, the SCC can be programmed to select its
internal registers using lines AD5-AD1. This is done either
automatically with the Force Hardware Reset command in
WR9 or by sending a Select Shift Left Mode command to
WR0B in channel B of the SCC. For this application, the
SCC registers are located at I/O port address “Fexx”. The
Chip Select signal (/CSO) is derived by decoding I/O
address “FE” hex from lines AD15-AD8 of the controller.

To select the read/write registers automatically, the SCC
decodes lines AD5-AD1 in Shift Left mode. The register
map for the SCC is depicted in Table 1.

Figure 4. Block Diagram of Two Z8000 CPUs

Table 1. Register Map

Address

Write

Read

(Hex)

Register

FE01

WR0B

RR0B

FE03

WR1B

RR1B

FE05

WR2

RR2B

FE07

WR3B

RR3B

FE09

WR4B

FE0B

WR5B

FE0D

WR6B

FE0F

WR7B

FE11

B DATA

FE13

WR9

FE15

WR10B

RR10B

FE17

WR11B

FE19

WR12B

RR12B

FE1B

WR13B

RR13B

FE1D

WR14B

FE1F

WR15B

RR15B

FE21

WR0A

RR0A

FE23

WR1A

RR1A

FE25

WR2

RR2A

FE27

WR3A

RR3A

FE29

WR4A

FE2B

WR5A

FE2D

WR6A

FE2F

WR7A

FE31

A DATA

FE33

WR9

FE35

WR10A

RR10A

FE37

WR11A

FE39

WR12A

RR12A

FE3B

WR13A

RR13A

FE3D

WR14A

FE3F

WR15A

RR15A

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