Zilog Z16C30 User Manual

Page 21

1-8

Z16C30 USC

SER

ANUAL

UM97USC0100

ILOG

Table 1-4. More Serial Controller Features of the USC

Transmit Control Blocks

A Transmit DMA channel can fetch the Tx CC frame length and other control info
for each frame/message, before the frame in the memory buffer.

Receive Status Blocks

The Rx DMA channel can provide the frame status (including CRC status) for
each frame/message after the frame. Optionally it can also provide the the Rx
CC frame length residual, although this is only useful in Rx DMA applications in
which software can read the number of bytes/words that were stored, from the
DMA channel.

Commands

Software can write various command codes to 3 different register fields in each
channel, to control the operation of the channel. Commands can be divided into
those that select a long-term configuration of a channel (like selecting which
serial character in a 16-bit word comes first), those that make the part perform
a time-sequenced action (like sending an Abort sequence), and those that
change the state of the part immediately (like purging a FIFO).

Software Reset

Software can reset a USC channel by writing a central register bit, similarly to
a hardware-signaled Reset.

Rx and Tx FIFO Storage

32-character FIFOs stand between the Transmit Data Register and the Trans-
mitter, and between the Receiver and the Rx Data Register. Fill level counters
track how many characters are in each FIFO, and independently program-
mable threshold values determine when DMA operation will be triggered to fill
or empty them, and/or when an interrupt will be requested.

Between Frames/Messages

In synchronous modes the Transmitter will do the following before the first
data character of each frame or message, and/or after the last one:

■

optionally send a 8-to 64-bit Preamble for PLL synchronization or mini-
mum inter-frame timing

■

send an "opening" sync sequence or Flag

■

After the last character from memory, sending the CRC accumulated by the
USC is optional. Thus, a CRC received with a frame can be sent back out
without being regenerated.

■

send a "closing" Flag or Sync

■

send a selected "idle" pattern unless/until the next frame is ready to be sent

Waiting for Software Response

Software can select 3 optional interlocks between frames, to allow it to do
real-time processing on a frame-by-frame basis.

UM009402-0201