Zilog Z80230 - Manual (Page 274)

SCC/ESCC
User Manual
UM010903-0515 Application Notes
267
Finally, an unpopulated 4-pin oscillator socket is included on the board with its output connected
to a single jumper/wire-wrap pin. This socket can be populated with a user-supplied oscillator and 
connected to various clock pins among J5-J15.
Sensing Which Serial Controller Channel is Connected to the Console
To use the software provided with this evaluation board, one of the serial controller channels must
be connected to a PC or a dumb terminal via the J1 and J13 connectors. Some versions of this soft-
ware may restrict the choice to (E)SCC Channel A or (M)USC, depending on your application
needs. There is nothing in the hardware that limits the choice of which serial channel is used for
the console. However, on the J1-J4 (J13-J15) side, there are two things that are special about the
J1-J13 section as compared to the others. One is the provision for a Non-Maskable Interrupt in
response to a received Start bit, as described in addressing on page 257 .
Software can use the other special feature of the J1/J13 section, after a Reset, to sense which serial
channel is connected to the Console port. A Reset signal (from power-on or Reset button but not
from the Reset-The-ISCC, address decode (and others) described earlier) places the "NMI" EPLD
in a special mode where the first Start bit on the Consoles Transmit Data lead causes an NMI. This
feature can be used in a start-up procedure like the following example, to determine which serial
controller channel is used for the Console.
For each serial controller channel that the software can use for the Console:
1. Initialize the channel.
2. Send NULL character to the channel.
3. Wait for a short time to see if an NMI occurs. If an NMI occurs., the current channel is
the Console otherwise go on to the next serial channel and try again.
4 Port0 (Clock 0 In) Port0
5 N/C N/C
6 Port3 (Rcv TSA Gate Out) Port3 (Rcv TSA Gate Out)
7 N/C (SYSCLK)
8 Port5 (Rcv Sync Out) Port5 (Rcv Sync Out)
9 Port2 Port2
10 GND GND
11 PORT6 (Rcv Sync IN) PORT6 (Rcv Sync IN)
12 Port7 (Xmit Complete Out) Port7 (Xmit Complete Out)
Pin Assignments of Controller Port Connectors (Continued)
Pin No J11:IUSC Signal J12: (M)USC Signal