Z16M1720ASG1868 Zilog, Z16M1720ASG1868 Datasheet - Page 159

• Manufacturer Part Number: Z16M1720ASG1868
• Description: IC PCMCIA INTERFACE 100-VQFP
• Manufacturer: Zilog

Specifications of Z16M1720ASG1868

• Applications: *
• Interface: *
• Voltage - Supply: *
• Package / Case: 100-LQFP
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

UM008101-0601
Table 18. Transmit Event Sequence (Continued)
In an interrupt-driven CPU transfer scheme, the SIO must interrupt the CPU
whenever it has received a character or needs another character to transmit.
A very short benchmark service routine, which assumes the exclusive use of
the Z80 CPU’s alternate register set for SIO interrupt handling, is provided
below.The numbers in parentheses are clock periods per instruction.
Before the service routine can be executed, the CPU must have its inter-
rupts enabled, finish its current instruction, and execute an interrupt
acknowledge cycle (19 clock periods). This optimistic benchmark takes at
least 68 clock periods per byte transferred, and severely restricts CPU
activity by permanently occupying the alternate register set.
To compare these transfer methods, the ratios of clock cycles used per
Kbaud to clock cycles available per second can be calculated. These
Event
DMA I/O write cycle begins
DMA terminates BUSREQ
DMA I/O write cycle ends
CPU terminates BUSACK and
regains control of bus
SIOSVC:
EXX
OUTI
JRZ,BLKEND
EXX
EI
RETI
; get transfer parameters
; transfer a byte,
; update parameters
; test for end-of-block
; save parameters
; reenable interrupts
Inter-event delay
(clock periods)
1
1
1
3
(4)
(16)
(7)
(4)
(4)
(14)
<   % 2 7 2 G T K R J G T C N U
Direct Memory Access
latency, bus occupancy
latency, bus occupancy
bus occupancy
latency, bus occupancy
7 U G T / C P W C N