Radio Shack TRS-80 PT-210 Service Manual page 25

I
POWER ON Reset
I
When the POWER switch is ON, a Reset signal of about
20
ms is produced by causing a delay in activa-
!!@
tion of lC*s input voltage "d" by C and R. A Reset signal resets the encoder, USART, and the data gate,
and a Reset signal resets pCPU and the clock. The timing chart as of POWER ON Reset is as follows:
POWER ON
+
5v
RESET
RESET
Schmitt Trigger Inverter
RESET
- K
Figure $9.
k t @
pCPU and Peripheral Circuits
The pCPU is made up of the block composition shown below:
Programmable Keyboard Control: Keyboard interface used for an @-bit pCPU. It scans each signal input
through the keyboard and converts it into ASCII code in accordance with the instruction from the
pCPU control.
8
E P ROM: 4K-byte E P ROM.
USART {Universal Synchronous/Asynchronous Receiver/Transmitter) USART is used for the peripheral
circuit, and programming is done through the CPU. USART receives parallel data from the CPU and,
after conversion, transmits it into serial data. It also receives serial data and, after conversion into
parallel data, transmits it to the CPU.
pCPU: The pCPU is an 8-bits microcomputer for parallel processing with RAM 128
X
8
bits, an l/O
port, an 8-bit timer/counter, a control circuit, etc. on one chip.
ROM and l/O port may be externally connector
l/O Port (l/O expansion port: It is possible to expand a 4-bit l/O port of I set to a 4-bit l/O port of four
sets by one chip.
Data is input from port 2 at the activati~n of the PROG terminal, processing is made in accordance
with the mode, and the data is then output through the designated port.