Zilog Z16C35 - 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 Register
FE01 WR0B RR0B
FE03 WR1B RR1B
FE05 WR2 RR2B
FE07 WR3B RR3B
FE09 WR4B
FE0B WR5B
FE0D WR6B
FE0F WR7B
FE11 B DATA 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 A DATA
FE33 WR9
FE35 WR10A RR10A
FE37 WR11A
FE39 WR12A RR12A
FE3B WR13A RR13A
FE3D WR14A
FE3F WR15A RR15A
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