Z85233 Datasheet, PDF (253/317 Pages) Zilog, Inc. – The Zilog SCC Serial Communication Controller

Application Note
Boost Your System Performance Using The Zilog ESCC^™
ESCC/SCC DIFFERENCES
The differences between the ESCC and SCC are shown
below:
ESCC ENHANCEMENT
1. Extended Read Enable of Write Registers
2. Hardware Improvement
- Modified WRITE Timing
- Modified DMA Request on
- Transmit Deactivation Timing
3. Throughput improvement
- Deeper Transmit FIFO
- Deeper Receive FIFO
- FIFO Interrupt Level
4 SDLC End Of Frame Improvement
- Automatic RTS Deassertion after Closing Flag
- Automatic Opening Flag Transmission
- Automatic TxD Forced High in SDLC with NRZI Encoding
When Marking Idle After End Of Frame
- Improvement to Allow Transmission of Back-to-Back
Frames with a Shared Flag
- Status FIFO Anti-Lock Feature in DMA-Driven System
PERFORMANCE BENEFITS
- Improves Testability
- Ability to examine SDLC status on-the-fly
- Improves Interface to 80X86 CPU
- Improves Interface DMA-driven system
- Reduces TBE Interrupt Frequency by 3/4
- Reduces RCA Interrupt Frequency by 3/4
- Flexibility in Adapting CPU Workload
- Reduces CPU and DMA Controller Overhead after
End Of Frame
- Allows Optimal SDLC Line Utilization
The differences between the ESCC and SCC are The advantages of the new features are illustrated in the
summarized by a new register, WR7' (Figure 1).
following examples.
RR7' Prime
D7 D6 D5 D4 D3 D2 D1 D0
Auto Tx Flag
Auto EOM Reset
Auto RTS Deactivate
Rx FIFO Int Level
DTR/REQ Timing
Tx FIFO Int Level
Extended RD Enable
Not Used, Always 0
One of the features that is offered by the ESCC, but not the
SCC, is Extended Read Enable. Write Register values
from the WR3, WR4, WR5, WR7', and WR10 can be
examined in the ESCC but not the SCC. This feature
improves system testability. It is also crucial for
SCC/ESCC differentiation and allows generic software
structures for all SCC/ESCC devices.
Flowchart 1 (Figure 2) shows a generic software structure
applicable for all SCC/ESCC initializations. Flowchart 2
(Figure 3) suggests a method for determining which type
of SCC/ESCC™ device is in the socket. This software
structure helps the development of software drivers
independent of the device type.
Addressing:
WR15 D0
'1'
WR7
'XX'
Figure 1. WR7' Definition
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