Zilog Z80230 - Manual (Page 275)

SCC/ESCC
User Manual
UM010903-0515 Application Notes
268
If none of the allowed serial channels produce an NMI, you may not have properly jumpered any
J5-J10 connector block to the J13 block.
Basic software should use the serial controller channel for the Console in a very basic, polled way.
Because of this and similarities between the (E)SCC and the ISCC, and between the (M)USC and
the IUSC, note that software allows the Console to be connected to either the (E)SCC Channel A
or to the (M)USC. It includes most of the code necessary to use any of the six serial controller
channels for the Console.
Notes on J4/Macintosh/AppleTalk/LocalTalk
The J4 connector is similar to the connectors offered on various Macintosh systems. The ESCC
and ISCC are well adapted for use with this port, and development of USC family capability for
AppleTalk/LocalTalk.
The J3 and J4 connectors cannot be used simultaneously. The J16 jumper block controls whether
the RS-422 driver for Transmit Data is turned ON and OFF under control of the associated
Request to Send signal, as on the Mac, or is ON full time, which is more suitable for the use of J3.
To put the TxD driver under control of RTS, jumper J16-J1 to J16-J2 and leave J16-J3 open. For
full time drive on TxD (and also the J3 RTS pins), jumperJ16-J2 to J16-J3 and leave J16-J1 open.
The J17 jumper block controls whether the reception of Data Carrier Detect and Clear to Send is
differential (on J3) or unbalance, as on J4. To use differential signalling from J3, remove all jump-
ers from J17.
On the initial Macintosh and subsequent ones as well, Apple did the unbalanced signaling back-
ward from the standard RS-423 and RS-232 polarity for the CTS lead (also called HSK and
HSKI). If you are developing code for Macintosh hardware, you can preserve Mac compatibility
by jumpering J17-J3 to J17-J5 and J17-J4 to J17-J6. This grounds the CTS- lead and connects the
CTS+ lead to J4-J2. It also (assuming a standard source at the other end) inverts CTS to the oppo-
site sense from that expected by the serial controller for functions such as auto-enabling. To make
the CTS input of the serial controller have its normal (low-true) sense, jumper J17-J3 to J17-J4,
and J17-J5 to J17-J6. This grounds the CTS+ lead and connects the CTS- lead to J4-J2.
The DTR (HSKO) is provided in the Apple
systems from Mac Plus onward and has standard RS-423 (and RS-232) polarity.
The DCD input on J4-J7 is provided in Apple systems from the Mac II and SE onward, and also
has standard polarity on Apple hardware. Jumper J17-J1 to J17-J2 to ground "+" input of the
receiver. The "-" lead is connected to J4-J7.
With jumpers installed to make DCD and CTS unbalanced, J4 can also be used for an additional
RS-232 serial link. Connect a "Mac to Hayes modem" cable to J4, and optionally a null modem
interconnect module to the other end. The cable internally grounds the RxD+ and TxD+ leads so
that RxD- and TxD- function like RS-232 signals.
Macintosh systems also include provisions for synchronous clock inputs. It is unknown if these
features are used by any applications or attached hardware. On all known Macs, the SCC’s TRxC